I see a lot of "my submissive cannot have friends" that are of one gender, or cannot have friend nights out. I do understand why those rules are put in place, however I believe that is a unfair statement.
I think its important that people, my sub included, have friends. I would call myself a friend of her, if i had one. There is a Dynamic that needs to be followed, however if it is all serious business and she can't come to me when she needs to discuss something, or simply just needs a ear to open to her...I would like to be that person.
You are your own person, have the right to set the rules for your submissive, if you so choose, but this might lead to the hefty sacrifice of your submissive losing a lifelong friend, or perhaps bringing a intervention to her (an awkward one at that...) if her friends decide to.
Perhaps....get to know her, find out her friends, and don't set up unnecessary rules from the start. It sort of shows a slight bit of jealousy that is not very becoming.