OK. Final update on this after all the feedback which I greatly appreciate.
Called around to the top schools that DD had considered going to before finally deciding to accept appointment at USNA. Essentially asked them for their "advice" in what to do about situation where DD would have to do PS and very frankly discussed implications of potential injuries, change of heart after PS, etc. Also very truthfully said that we had strongly considered/wanted to go there as well but did not want to hold hostage a spot that we may not be using and keep another deserving student from attending off the waitlist. Always asked for an associate / assistant dean at each admissions office. My wife had approached someone from the admissions office at one of the schools during an admitted student visit and brought up the topic and got a fairly hostile response. Needless to say, even if we did not receive an appointment at USNA, after that interaction we scratched that school off the list with a bad taste in our mouth. In retrospect, probably was a junior staff or otherwise in the admission office but probably good idea to go higher up the administrative chain for this type of conversation should you choose to take this route.
There were 4 schools in total I had called. We had already turned down offers from some of the schools lower on DD list. Of the ones called, 2 were highly regarded state schools, both ranked in the top 30 or so of top schools in the country. The school lower on the list said no problem at all in terms of putting down deposit and having change of heart later. They have these sort of things often and they usually plan for a certain amount of attrition during the summer for this exact scenario. Also, they said for this such special situation, they would completely understand. The more competitive of the 2 state schools said essentially no....you have to choose by the deadline.
Of the 2 private schools, the one in the top 10 of the country said essentially no but if things did not work out for some reason(e.g. injury), could re-approach them and see if they could accommodate given all the wait list and such even late into the summer. The other private school essentially said no as well.
In the end, we are going to put a deposit down with the solid but 2nd choice state school as a Plan B. They are open to it and fully understanding and supportive. Given their support and openness to it, makes me think that this would be a great alternative that would welcome DD in the unlikely situation of an injury or change of heart. Would be very happy to be there in this scenario and grateful of their openness.
That said, there's also the consideration that since it's not the other "top" school that she could potentially have chosen over USNA, the possibility of using it as a "escape hatch" during the rigors of plebe year are lessened I think.
Thanks to all in the SAF for your advice and support!