That is a horse born to be lame. Her hind legs are over angled and she is severely sickle hocked and very light in bone. She is over at the knee in front and it looks like she has an issue with the right knee.
To add to her troubles she is trimmed with low heels and long toes.
I suspect this horse is developing spavins. I look at this horse and can only think that if she is always uncomfortable the kindest thing may be to put her down. I know that is not a popular thing but to live in discomfort is not a fun life. Maybe not now.. but this is a horse that won't improve with time. Keeping her out 24/7 will decrease her discomfort.. so see how it goes.. but horses are expensive to just keep around and at 11 you are looking at a lot of money and a lot of years.