I heard your problem,and I think that the only way to solve this problem is a face-to-face talk with her.
Tell her what you think and listen to what she replies.Only in that way can you two find a commonground and understand each other.
If you don't reach a commonground,you should try to tolerate something you don't like.You said you are getting on well with you cousin,that means you like her.If so,it won't be difficult to forgive her.Sometimes someon has to make some compromise.
Wish you good luck on solving the problem with your cousin.
寫的有點多了,自己挑一挑,刪一下吧