First....congrats! You must be thrilled, especially since it might end up being on the same date.
But I, too, am having a bit of trouble with your rationale on this one. Clearly, it's your guest list, but I'm not seeing much in the way of logic that would dictate SIL should be invited. Why would your DH want her there if she causes trouble? Also, you say you don't want good good SIL to take the blame, but it sounds like you had to talk her into issuing the invite, so I'm assuming she was willing to accept that blame.
I just have a problem with reinforcing inappropriate behavior. Also, I think it'll be very tricky wording the invite to make it clear it's her sans daughter. She sounds like the type that might bring her anyway and then shrug off the "misunderstanding".
Good luck with this!