Whilst Judie Dench is in the correct age group, she would’ve gained her commission in the regular army as 2nd Lieutenant in the early to mid 50’s. Whilst that’s possible as part of the WRAC.
In the early ‘70s the Greenfinches were out on mobile patrols but were unarmed.
The WRAC did have the rank of Brigadier, but that was solely within the remit of the WRAC.
The first female to reach Brigadier on merit as part of the regular army wasn’t until Patricia Purvis in 1997.
In your timescale the only female Brigadier was Helen Meechie, though it was only an administrative/honouree role, though her predecessor was well respected by combat troops.
It might be hard to get a female in the role of UNIT before the 2000’s.
For the role, the experience required would have to served at 2IC at the very least of a force such as 5 Airborne brigade and/or some senior level experience with those nice chaps at Hereford. Having ‘Det’ on your CV would also be a bonus.
All pointing to ‘highly unlikely’ a female running UNIT.
Possibly Edward Woodward as Brigadier Sir Fraser Fairbairn GCB, GC, DSO, DSC, MC. Lt Col Angela Reynolds as 2IC, though even that would hard to push.