The same themes resurface in this, her latest stage premiere - reworked from its original Sony Award-winning radio version - which finds two fraternally- linked branches of the same Welsh/Scottish family holidaying together in Wales, all the action unfolding on the symbolically palindromic date of 16 June 1961.
As this numerical pivot craftily hints, for both the Williams clan and the country at large things seem to be hang in the balance. Cusps, dualities and dialectics abound: between Fifties post-war conservatism and the nascent social and cultural upheavals of the Sixties; between childhood, adolescence and adulthood; between love and hate, aspiration and acceptance, romance and reality, interior and external worlds, men and women ...
Standing half-bewildered, half-knowing in the midst of these tensions is Macdonald's pubescent, characteristically square-peg-ish central character, Rena, so exasperated with her relatives that she repeatedly and urgently attempts to summon the bogeyman figure of a supposed serial killer, whose exploits have been enlivening the Scottish press back home, to dispatch the lot of them.
The decidedly dark edge of this childish wish-fulfilment fantasy is an example of Macdonald's skill at layering and inflecting the drama's emotional narratives, conveying the push and pull of incompatible yet coexistent longings.
From a list of the characters' various interrelationships, their tale might sound suspiciously over-burdened and schematic. Rena's roving-eyed father, John, and her aunt, Dora, are having a long-term, open-secret affair; her mother, Ailsa, is feeling doubly threatened and insecure thanks to the newly-blossomed beauty of Dora's teenage daughter, Rhiannon, who is secretly in love with a married man, while Rena herself resents her younger cousin, Noelle, for looking down on her and putting on airs - and then Dora's eldest son, Gareth, discovers not only her infidelity, but his father's tacit resignation to it.
Macdonald, however, mixes all this within a convincing realisation of family holidays' familiar glitchiness and intermittent boredom, using the adults' constant resort to swapped snatches of popular song or forced jocularity as an all-too-revealing cover for the seething undercurrents. She has an enviable knack of lending seemingly the simplest of lines a multiple resonance, while avoiding the plod of overtly self-conscious intent.
This layering effect is mirrored by designer Jacqueline Gunn's stylised version of the cove and overlooking cliffs which form the play's setting, with many scenes involving characters espying or overhearing one another from unseen vantage points. On opening night, however, the multi-facetedness didn't permeate quite so integrally through the performances, a degree of stiffness rendering the dialogue's shifts of tone and compass sometimes less than fluid.
All the characters, though - with 12-year-old Natasha Gray's Rena deserving specially honourable mention - are developed and defined forcefully enough for this aspect of their delivery to ease up as the production runs itself in.
Until 6 June (bookings 01382 223530), then at the Tron Theatre, Glasgow, 17 June to 11 July (bookings 0141 552 4267)