Wow, yeah, I'd say you both let your daughter down. Your ex is mistaken if she thinks she can get this worked through with the legal process in this time frame.
Someone needs to make a proposal here and that someone would be you. Rip the July page out of a calendar, mark it up and send it to your ex and to your ex's lawyer. Request they respond with a counter-proposal by Friday.
Tell your daughter that summer school threw a wrench into summer plans and you're (belatedly) working on it and that she will have time with her mom.