Sprained leg?

[StillMedusa]

Yesterday my nutter puppy (well 14m old) was off lead and playing with a dog when they sort of crashed and rolled.. and she yelped, sat still for a few mins looking pained. Got up and carried on our walk but yelped again when she did a fast turn running around, so I took her home. Had a good feel all round and couldn't detect anything major but took her for a very gentle on lead walk this morning.
This evening she was desperate to go out and was running happily but when she did a fast turn (again playing) she yelped and sat down again. Needless to say we went home. She's not limping exactly but I do think she is walking carefully on that back leg. Tried to ring the vet but they were closed (after 6) She has eaten her tea fine and is now snoring.

Obviously I'll give the vet a ring, but does it sound serious? I'll keep her on lead and minimal walk tomorrow (have to go out as she won't poo in the garden). Is there anything I should be doing for now?

I have to add that she is a total drama queen and screams if she gets a twig in her fur, however I do think she has hurt herself this time :(