Since the parvo we haven't been abl to keep her weight up some days she looks filled out then other days you can see her ribs and she eats al day long if you let her just wondering if anyone has suggestions

Sadly parvo survivors usually have life time health issues. It sounds like that's what's going on.

Is she a healthy weight, or does her weight dip considerably when she's "less filled out"?

Have you talked to a vet about this?

I agree, Parvo survivors do tend to have a hard time rebounding, Be sure to feed a high quality puppy food, check the feeding instructions to be sure you are feeding the right amount and a blood panel at your local vet to check for any underlying organ issues is a good idea. After pulling through parvo, you don't want to take chances now.
I really hope she does well for you.