Long term diarrhea can stem from so many things....bacterial infections, viral infections, fungal infections, worms, damage from worms, the diet of the bird, stress, a change of feed or just the feed itself.
What did you worm with? There could still be worms.
Also, after a worming, I always pump them with probiotics for at least a week following. Then I use them a couple of times a week anyway.
Too many vitamins and electrolytes will cause diarrhea as well.
Depending on what you wormed with, you might consider another wormer just in case. Then get them on probiotics. These can help not only with boosting the immume system but to heal any fungal infections. Add a good vitamin supplement to their diet. I use Calf Manna Performance Pellets in the feed. I have never had any trouble with diarrhea with this supplement.
If the bird still has diarrhea, you might try an antibiotic on her. She could have something like E.coli or an Enteritis of some sort.
All our local store had was Piperazine so that is what we have used the 2 times we have wormed. They now carry Rooster Booster Multi-Wormer Triple Action. It was about a month ago that we wormed. Is it too soon to worm again? Would that be an ok one to try? I don't know why I didn't think to follow it with probiotics, I will get some. Thank you all so much!