OP, I'm not muslim, but at my family's church you are supposed to wear a headscarfe in church, for a woman to have her head uncovered in church is considered sacriligous to them. I stopped wearing them when I was 18.
Over the years when I have visited them and gone to church with them I have had pressure put on me to wear it. I will accept the other restrictions, wearing a below knee skirt and not trousers, keeping shoulders covered, tops modest, wearing a paler shade of lipstick rather than a really bold colour, etc- but only because they are things that I don't object to doing, and would, at some point or other, do myself. I wouldn't, however, ever wear a scarf on my head at any other point in my life so won't wear one in their church.
I also have [shock, horror] sat with my DH at the back of the men's aisle rather than leaving him to it - he doesn't however speak a word of their language. I'm sure a large part of the congregation thinks I'm damned to hell - even though I attend an Anglican church regularly and actually assist with communion. I keep having 'but you know what the true faith is' thrown at me. 
So I do understand (to a small degree) what you are going through. I hope you find the strength to not be bullied, because that is exactly what she is doing.