My young dog is very excited when I take her out of her crate. She jumps around and mouths my hands when I try to put on her harness or leash. How should I handle this situation?

This is very typical young dog behavior.

You could use a slip lead when she exits the crate and control her that way while you put on her harness.

I have an 8-month-old GSD right now and I taught him touchpads from the time he was a baby and so I choose to have him put his feet on something when he leaves his crate and then I can put his collar or harness on without much of a struggle. Don't forget to use food rewards for this! It works very well and he loves putting his feet on things.

I try to pick my battles with my dogs and it's much easier and more fun to reward cooperation than to try to wrestle with an excited young dog. :)

I hope this helps.