Hi Merlin, and welcome to the site
I think it's a question of defining "straight"...
Would a truly, 100% straight woman be interested in having a relationship with a butch? I think not.
It might be a matter of where you found her on her own personal growth curve. Most people (including myself) would have called me straight until I was in my 40s. For a variety of reasons, including some I wasn't even aware of myself for a long time, I pushed down my own sexuality and went along with what I was "supposed" to do and want.
It took me a long time to come out, even to myself.
Maybe that's true for them too...