Ligament and Tendon supplements?

I took my horse to the vet today to find out what those bumps were on her legs. She said its old scar tissue like she had tight tendons when she was born and they cut them to loosen them for her. But there's no evident scar to prove that's what happened.

I asked my vet if she was sound for barrel racing. Because she already does it and likes her job. She enjoys getting to be able to run. She said its a toss up, she could get sore a few months after barrels start or she could get sore 5 years down the road. She said if she starts getting sore when I barrel race her stop barrel racing all together. She said the soreness isn't anything that can't be fixed. But repeated soreness will effect her down the road.

I am looking for something to like work with her tendons to help her move and flex easier and better. Along with support boots and being careful she should be okay. I don't know if she'll get sore that's why I'm trying it out for a little while.

I'd like your opinions on that too.

Anything you think will help her tendons or anything else please suggest it.