My SO is similar size, maybe an inch shorter, very athletic, and has ridden cross country more times than I have. Her MOA number is a tiny fraction of mine- from more than 30 yrs ago- and she's owned several BMWs. We did the Morton's rally last weekend, played at a good clip in the VA mountains and did a nice 300 miles in the rain coming back- very nice to have an SO who rides well in any condition. Had so much fun I bought her a new Schuberth she was admiring...

She rides now an R1100S that I modded with bar backs, a bigger screen and a few other items to make it more useful as a touring bike. She had, hated, and sold a K75 (too tall) and would happily buy another airhead if they were made again- that was her favorite. She has no interest at all in current low models of R bikes or indeed any other full size bike BMW currently makes- though she has not yet tried the 800GT which easily has enough power to run with others while touring. Height of the bike is her explanation. I have joked with her about modding a S1000RR into her next touring bike because she complains her R1100S is slower on corner exits than my R1200RT- its the only BMW she sat on that she says is low enough. She also complains that even her R1100S puts her on the balls of her feet at stops (it does) though it looks almost toy sized next to my RT or K bikes...

We have female members of our local BMW club who are taller than her yet on J brand cruisers for the same reason.

BMW fails to get that many women are either not strong enough or are simply put off by all their tall models- and that low option seats are an inadequate answer. R's in general are top heavy and do little to make life easier for shorter folks, especially newbs- their poor low speed handling (bad first gear ratios, funky dry clutch, etc) doesn't help either- anyone who owns one knows its a pita in traffic compared to many other bike designs. I'm a typical size 6 ft male and find my own RT top heavy compared to BMWs K bikes that I also own- but I sure like its weather protection, easy maintenance, engine durability, comfort for long miles, etc etc

She will need adequate power if she wants to ride with you but a 750cc V twin Honda bought used for $4K can easily do that.....If you've got a cruiser bias, I'd rethink it- they sell more of those to women than BMW sells in total. Where I live essentially all female riders are on cruisers or sport bikes.

Her bike, her pick...You win only if she's happy with the result....