Re: non traditional 'girls' party
If she doesn't want a mehndi, I would respect that.
My friend who got married last year didn't want one either. She had a black and white party. Everyone was asked to wear black and white. She wore red. Most people were in dresses, some saris, some shalwar kamizes. It was women-only, so people who would not otherwise had a lot of fun dressing up.
There were various games and things, and a sit-down dinner. No music.
I definitely missed the feel of a mehndi, but it wasn't her style and it wasn't what she wanted, and I don't think it would've been fair to impose that on her. There are so many other opportunities to attend the traditional stuff. If someone wants to be different, let her.