unsubscribing is probably your best bet(when you see their post in your news feed click on the x and look for the unsubscribe option), however I can tell you this is a form of control, it is the equivalent of telling you who you can be friends with and who you cannot, I have FB with a bunch of EF bros and my husband knows it and he has his and his friends and yes some of them are hot and I dont care, why? because if he has them on facebook he has a way of contacting them, therefore if he wanted to he can email them, call them, text them, etc. Having them on FB wont make him any more or less prone to cheating on me with them, also, there will always be a chick hotter than me, and another hotter than her, and so on, so I cant hate on them and control him because of my own potential insecurities.
I can tell you this can be the first step down a slippery slope, she will see she can control who you talk to, next thing you know she'll wanna control where you go and who you go with, I know you have to be flexible in a relationship but this seems like a first step to potential issues.