am I over reacting ?!

Ch
So basically my OH's brothers gf is all over my OH Facebook status saying she can't wait for a cuddle when baby is here...
Okay... here's the background...
I met her roughly two years ago at my partners birthday meal. The whole time I was trying to talk she talked over me and about herself so yeah we defo have nothing in common and I don't like her at all. Since then when we have seen each other we have not spoke a word and she has not bothered to speak a word to my son (previous relationship baby who's now four and my current partner is now bringing him up) but all of a sudden she can't wait to get her chubby fingers on our unborn child just because it's going to be 'blood related to the family' (OH brother and girlfriend has this obsession with blood related family only)
So anyway I'm bloody fuming and do not want her to lay eyes on my baby let alone give her a cuddle! 
What do you guys think?! 
My OH and I have argued about this and he's thinks the family should always agree and do as she says so she doesn't threaten to take the brothers kids away (which she does when anyone disagrees with her ) 

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