I would actually have an issue with it.
My concern would be with bolt tension, or more specifically the lack of proper bolt tension. I don't want a bike falling apart because the female mechanic lacked the strength/body mass to adequately torque the bolts. I'd be ok with a female mechanic assisting the main mechanic with things like changing tires as long as she is not the one tightening bolts requiring high nm.

Even so, I'd feel like I had to check/torque all bolts every time I got a bike out of a LBS who had a female mechanic which would make me a hell of a lot less likely to go there.