Ladies Bikes - What are you riding?

This is surely more to do with body proportions/arm & torso length rather than the actual size of your hands.

Brake levers especially modern STI type only come in one size (I think) and even children manage to use them. Handlebars & stems is not really going to effect how your hands fit around the levers. Even for use in the hooks of your bars, the brake levers can be adjusted for closer reach.

If your talking stems & bar changing. Your really talking about a frame being too long for you. Try getting your stem higher, stack more spacers and use a riser stem.

Your assuming that mantrap is using STI's when chances are that on her 1960's bike will not have these.

My advice to mantrap would be if she lives in London got to one of the shops that is known to give trusted advice to women or to head to on of the compass drinks when Nhatt is at souths or longandwinding is at wests as both have very different but very good experience/advice on bikefit for women.
If not in london try your local IBD for advice as you know what they are not all staffed by sexist, condacending men who belittle women customers.