I'm assuming that your daughter is going to pay for part of the house rental? If so, then it's as much her getaway as yours and hubby's, and I would find an excuse to send her a casual text mentioning the trip. Something like "Oh, VRBO just sent me a reminder about the rental in August--are you still interested?". The ball would then be in her court.
If you and Mr. Capricorn were going to foot the entire bill, then I'd say go ahead and cancel. It would've been your gift to her and as such, you have the right to rescind your offer. I'm sure we SZers don't have all the details but it's possible if your daughter is *really* hurting, it's going to take more than a few months to get to a point where she wants to be around you for more than, say, a shared meal or a single night out.
Whatever you decide, good luck!