Well, I think you're a sweetie for coming on here and asking your question the way you did. You aren't ranting and raving and screaming about it. You see it in a realistic light, and you DO have a good attitude about it all.
I think it's perfectly normal for you to be upset, even though you see the logic of your daughter having a positive relationship with him. It probably stirs up all the awful feelings this man put you through before.
However, I will bet that you are actually thinking about your pregnant daughter being hurt by him, like he hurt you, although it's really not the same. You are probably just wishing you could protect her from his cruelty, like you wish you could have done when she was younger. The new baby surely has triggered this.
I don't think that you should say anything to your daughter about being upset. I do think that perhaps now is not the time to send your younger one over there. You could give yourself time to get used to this other woman being around your grandbaby before you do that.
More than anything, keep your good attitude, and give yourself time to get used to the idea of having to share with the "interloper". Your good attitude is what will get you through it. Terrible attitudes eat people up inside and mess up their psyche, and make them miserable to be around and make them seem mentally unbalanced. Those are the people who you wonder if they caused most of their own problems in their prior marriage.
If it makes you feel any better, just keep it in your mind that she has to live with all his awful traits, and that one day he'll screw around on HER and make her feel terrible like he made you feel.
Dawn