I am no expert at all, but if it is mushy and not hard and there are no changes in her behavior that would indicate that she is stressed, in pain, or sick, I would think that she is ok and just maybe banged it on something like a bruise or got it pinched in something. I would NOT try to drain it because it will probably just absorb the extra liquid back into her body when it is done healing, and opening it up would make it easier for infection to enter the body. However, there could be a small infection in the body already, but it looks to me like the body is dealing with it ok if it is not getting worse like spreading, changing color, or causing any problems for her. Continue to watch her very closely. Whatever you are doing seems to be working so far. :happy: Just make sure you keep her at the right temperature and her living quarters are clean so she can fight things off. It is important that she is not stressed so she can have a good immune system. It is a very good sign that she is eating through this.
Make sure she is getting enough calcium in her diet by feeding her the right combination of foods for her. You may want to see her care sheet again and look in the food area for specifics. You don't want her to develop leg problems from eating too much phosphorus and not enough calcium. I don't know if you may need to dust her food with a calcium supplement or gut load her food before you feed it to her. There is an area about that too. I don't want to see her get "red leg". You may find that you are fine with what you are doing.
If you would like to have a professional opinion, there are veterinarians on here regularly and they are indicated on the first page where all the people who have been on here in the last 24 hours are listed. They are listed in the color which indicates they are veterinarians. You can ask some of them if you would like. They may know better than I would.
You have a very nice and healthy looking salamander as far as I can tell, and I know you care a lot about her. I truly wish you the best of luck, and hope you keep us updated!
Good luck,
Critter Mom