Well i wouldn't go spreading her secrets and stuff as well, that'd just bring you down to her level.
No one can make the decision for you, at the end you just have to do what you feel but if i were to offer my advise it would be to leave her and find a new friend.
If she nags you and asks you why then just tell her and say that she blew her chance and really took advantage of your loyalty so you're moving on.
If she does bug you then you could be really cheeky and say "i am on my period dont piss me off!" just for fun
Good luck with it
I hope it works out okay x