The spirit of a teenager lives on in Sharman Macdonald, even though her hair is dramatically streaked with grey. She is now 43, roughly the same age as the mother in When I Was a Girl I used to Scream and Shout, her first play and the one which established her reputation as a playwright. But things have a tendency to recur in her life as well as her work, and her rumbustious wit, like her career, shows no sign of abating.

It was Alan Rickman who read that first play when she sent it to the Bush Theatre 10 years ago. Now he is directing her latest, The Winter Guest, which opened on Monday. Like When I Was a Girl, this play is set in a seaside town on the west coast of Scotland and concerns both burgeoning sexuality and the fraught relationship of a mother and daughter. But by now the canvas of Macdonald’s work has broadened to span the generations, from a couple of 12-year-old boys on the beach to a pair of octogenarian ladies on the promenade. And with this broadening has come a darkening: the shadow of death has crept into the picture and colours everything.

The Winter Guest came about because of a dinner conversation between Rickman and Lindsay Duncan (his co-star in Les Liaisons Dangereuses) about her mother, who was dying. It occurred to Rickman that the stories would make a fine play, and that Macdonald was the woman to write it. Macdonald was hesitant, never having been set a subject to write about, but agreed to do it. "I’ve gone very far from the original idea," she admits, "but if it weren’t for Helen [Duncan’s mother] this play wouldn’t exist."

Rickman and Ruby Wax, his partner in their company Raw Produce, gave Macdonald complete artistic freedom, and their collaboration proved fruitful. "After each draft, Alan would write me long letters in beautiful but undecipherable handwriting," confides Macdonald. "I’d sit there for hours trying to make out what he’d written, and having to be very slow and methodical paid dividends. He never even identified a problem, he just implied it, so I never felt I’d failed. I was given the safety net to go on being risky."

The effects of being risky in this case led inevitable back to Macdonald’s distinctive personal landscape, much of which can be traced to her own history. Born in Glasgow, she led an itinerant childhood following the fortunes of her engineer father, but has strong memories of Ayrshire, where she could see the isle of Arran from the kitchen window. "I used to go down on the bus every Saturdayon my own and play with the sea," she recalls. "My mother said, ‘I never noticed you making use of it,’ but it has appeared in almost all my work." Macdonald went to University in Edinburgh, where Max Stafford-Clark was revolutionising theatre with his Joint Stock methods. She became an actor in 1972 and moved south to live with the actor Will Knightley, with whom she has two children.

She appears to be one of a generation of women who did succeed in "having it all," but the suggestion that she has effortlessly stage-managed her life reduces Macdonald to an extraordinary state of emotion - is she laughing, or crying? "I am very privileged," she says when she is again able to speak, "but it has been at a cost. If you’d ever had a child on one breast and a commission to write, you’d know... I often felt I wasn’t doing either thing properly."

Macdonald’s oeuvre to date has mapped with exquisite wit and compassion the pain, contradiction and compromise lived by contemporary women. Now that her parameters are braodening, she is turning her all-seeing eye to men. Lou Stein, the founding father of the Fringe, who commissioned Borders of Paradise for the Palace Theatre, Watford (opening 16 March), confesses to some surprise when Macdonald announced that her inspiration was a group of 15-year-old English boys she had watched surfing in Devon. The sea remains the constant factor, but the familiar Macdonald terrain has changed somewhat.

"The play is about this very fleeting, very special time I remember when I was a teenager," says Stein, "There are things you’re feeling that you don’t quite understand, and in a year’s time it all changes very quickly. The interesting thing for me is how much it reflects on adult issues of life change. After eight years at the Palace I’m going freelance. My fears and hopes of the future are kind of similar to that moment of shedding childhood."

Having a 15-year-old son has given Macdonald a new perspective on adolescence, and a specific insight into the male version. She perceives that changing mores provoked by feminism force boys now to confront issues their fathers never had to ("They expect to be asked out by girls for one," she says archly). But her main concern is for the uncertainty of the future in a society overshadowed by decline. "When I was that age I had no thought of unemployment - even though my father was made redundant. But for me there was always going to be work. There have been times when my son has said he can see no hope. And he’s a privileged, middle-class kid, so what’s the knock-on effect?"

Perhaps Macdonald is fascinated with adolescence because it contains the blueprint for frightening and exciting life-changes: she, too, is in a time of flux. With two new plays opening in the space of of a few weeks, it is a time of consolidation but also of judgement. The signs bode well, but the playwright betrays a surprising lack of confidence. "Outside my hotel in Leeds I can see ‘the Sharman Gates’ - I think they’re the gates to a cricket ground. But it seems pretty significant. They might open. Or they might not."

In the humorously humane plays of Sharman Macdonald, a daughter’s place is always in the wrong. She excels at portraying the difficult bond between fortysomething women and and their badgering mothers whose pained love for them takes the skewed form of quirkily garrulous fault-finding. Tact is not their forte.

The Winter Guest, her new work, premiered in Alan Rickman’s beautiful production at the West Yorkshire Playhouse, plays tragicomic variations on a relationship of this kind. The daughter Frances (Sian Thomas) is once again a widow before her time, with a son (now adolescent) and a life stalled by the memory of her husband. Wrapped in a defiantly non-PC fur, mistress of the mistress of the airy Scots put-down ("If you want movement, Frances, make a film," she says of her daughter’s professional photograph,) Phyllida Law’s consummately acted mother shows you a woman who would like to make a friend of her child. Up to the end, though, her efforts to do so are amusingly counter-productive.

The action takes place one February day in a seaside town on the west coast of Scotland, the dun hues of the rocky ice-bound beach dreamily realised in Robin Don’s remarkable set. Preoccupied by death and the need to assert a human resilience in the face of it, the play shows the mother-daughter pair in juxtaposition to other generation-spanning couples. At the oldest end are a pair of prim biddies (Sheila Reid and Sandra Vow) who positively live for the funerals they attend. At the youngest, there are a pair of pre-pubertal, foul-mouthed schoolboys (John-Ross Morland and the brilliant David Evans). In betwen these poles, Frances’s son finds tentative adolescent love and a possible way of exorcising his father’s paralysing posthumous presence.