59 races is a lot. At what age did she stop racing?
You can look at things 2 ways. Either she is used up from a prolonged racing career or she has great longevity, is well put together, uses herself correctly, is able to recover quickly, is athletic.... She might have some nagging aches that you need to keep up on but I'd be more inclined to use her if that's what she's telling you.
I have a 24 year old OTTB gelding that raced until he was 5. Don't know how many starts he had but other than some shoulder stiffness, he is good to go everyday.