I was riding her yesterday and after 10 minutes she went lame. We were trotting and she suddenly rushed as if something scared her or like she rushes when she trips. But she didn't trip... Well I went down immediatly, because limping was quite obvious, but I couldn't find anything wrong with her that day or today. No part of her is swollen or warm or injured. She'll rest for some time now and I hope she'll be better in few days. I really don't like this kind of lame horse... When I can't tell which part hurts!
When should I call vet if she doesn't get better?