When are you leaving for holiday? My advice is to keep your Bullie as still as possible for a few days at least. This means limit his exercise and if possible keep him confined to a crate so that he doesn't try to run. That should give it time to heal...if he is acting mostly normal he probably just pulled something and will be fine in a day or so with rest.
Keep an eye on him though.
I agree with James...To confine her to a crate...So she allows herself time to heal. For they will go about as normal as they can. And they really need to rest that leg...I am hoping you will have a few days...Before you actually leave. That you can do this...So you will be able to leave without as much concern for her leg...
I also might ask if they could...Not put her out with the "play group" and leave her more in a confined area for most of the day...With maybe a walk with a staff member. Verses playing with roudy dogs...Which could cause her leg to become more of an issue...See if their willing to go and give her walks...Verses playtime...To let her heal a bit...I myself would worry she would do more injury to her leg...During romping with other dogs...
A vet won't x-ray a leg...Unless they feel it deemed necessary. While on vacation...I called the vet that was listed on the information packet of where we were staying. And they opted not to even see our bulldog. Since he was not showing any other signs other than not putting weight on his back leg. And he came through without needing to be seen. But as soon as I seen him limping... he was crated...For his own safety to not cause more injury to his leg. And that giving him rest...Was really all he needed...So maybe you'll be so lucky and find the same situation with your bulldog...
Good luck and keep us updated...On how the leg is in a few days...