S.B.
First I would check her paw for cuts or glass (maybe broken lights?). If I didn't see anything, I would probably take her to the vet. If it were my dog, I'd probably give her another day. But seeing as it's someone else's dog, I'd probably take her in today.
Our dog developed a sever limp after having a minor surgery. I didn't think much of it at first. Called our vet over (she's a neighbor) and she thought it was something EXTREMELY serious. Took my dog in the next day expecting to have to make some tough decisions. Under proper lighting and with all the doctor tools, the real culprit was easy to spot...the bandages had rubbed a large blister on the side of her paw.
You never know. Better to err on the side of caution.