Joan, I agree it's true that some men fear strong, independent women, and seek out those who choose, for any of a number of reasons, to be dependent to a greater or lesser degree. It takes all kinds, and God made them all! There are also men who like strong women but would prefer to complement rather than compete with their partners. Might could be that your sister, perhaps unconsciously, puts a tad too much effort into proving she's the better man - and, from your description, she might well be!
I rather enjoy the company of a woman who takes care of herself with quiet confidence....and consider it quite a compliment when such a woman chooses my company. I'm sure I'm not the only guy like that.
Yes, very likely. She works in a "mans's world" and is always having to prove that she can maintain her professional status as a woman with integrity (not sleeping around to get a promotion, which is VERY common). It is VERY difficult for a professional woman to move up on the career ladder without losing their integrity.