Need Advice for very tiny rescued kitten who has diarrhea

My little Bambolina is about four to five weeks old, weights 411 grams.  She has been to the vet, has been constipated, underweight, undernourished, dehydrated at various times over the past couple of weeks, when rescued.  She's been syringe fed, bottle fed and now on critical care kitten food.  She didn't have a good prognosis two days ago but suddenly put on 50 grams in two days more than she did in two weeks.  She is still a couple of ounces under a pound.  Over the last two days, she is climbing up our legs, running around, playing with her toys, yelling for food, using the litter.  BUT her diarrhea is getting worse and  WE NEED HELP!!!   We are trying pumpkin mixed with her food but not helping.  Any advice?

Has she been wormed and checked thoroughly for the harder to find parasites like tritrich which requires a special test? Parasites are the most common cause of diarrhea in kittens.

Yes, if an in depth parasite test has not been done, I would start there. It is called a PCR GI panel.
If all comes back negative, I would run a cobalamin test and see if she has an Absorbtion disorder.
A food allergy/intolerance could also be to blame.

I am actually looking for natural remedies to combat her diarrhea.  We are trying pumpkin, wheat bran and Gerber's Baby Rice Cereal.  I was wondering if anyone else had something that worked for them.  Her diarrhea was bad yesterday and then got somewhat better during the night.  

If she has parasites, then no natural remedy is going to help. Constant diarrhea in a kitten this young can be dangerous. Please take her to a vet.

Vball91 is 100% correct.  And the chances are this is diarrhea from a parasite and untreated it can be fatal in young kittens.  They can literally go into intestinal failure and die.  Bring a stool sample with you to the Vet, and do not delay treatment.  Given her age the vet will probably want to start treatment immediately even without a test result.

Just chiming in to strongly agree with vball91 and stephenq.  There is no natural remedy that can or will help if it is a parasite. She has to go back to the vet and be tested and treated.  It is EXTREMELY likely that this is 'all' that is wrong, and if so it can be very very easily treated.  However, there is no natural or home-made way to do so. She needs a vet. As stephenq 100% correctly notes, this could quickly develop into a very serious situation in a kitten so young, which would be a true shame given how easy it is to treat once diagnosed properly.