Yes, it can damage her joints. If she jumps around during play, that's no particular problem, but I wouldn't be encouraging her to jump like that - especially repetitively. Better that her crate goes back on the ground
The reason that it can be a problem is because she is still growing. And that means her growth plates are still open (probably still
visibly open). Growth plates are those soft areas at the ends of all her long bones that allow for growth. But being soft, they're also very vulnerable to injury

And the sorts of things that injure are repetitive stresses (you shouldn't take a puppy on runs or extended walks, for example), impacts (jumping) and extreme exertion such as weaving (as in agility).
The growth plates will close and harden somewhere between 14-18 months of age. Obviously, that is when she will be finished growing. From that age onward, it's safe for her to jump, but until that time, I really wouldn't encourage it. What she does herself in play is fine, but it's best that you wait till she's mature before encouraging her to do more than that.