This is very difficult for you obviously but I should really try hard to work out what it is that bothers you about this girl.
My mum in law HATED me from the first moment we met and continues to do so with a vengeance. For various reasons there is no longer any contact at all between our family and hers but her venemous hatred of me is one of the main reasons.
I can look back honestly over the years that her son and I have been married and say that I've been good for him and he's been good for me. But her hatred has continued.
Your gut feeling might be correct in which case you should stick with it BUT, there's a chance you could be wrong. So, if you don't want to lose your son over this you should really find out what is bothering you or else...zip it!
By the way....don't panic! She may just be passing through and before you know it another young lady will be visiting you....so hang loose!
One more thing whilst I'm here.....saying or doing something unkind or unpleasant to this girl is something you can't go back on, won't be forgotten and will likely not be forgiven. The pain of rejection from someone is as real as stabbing them in the heart so...tread carefully...please!
Best wishes and be careful!