Olya, I don't have any personal experience, but I did find the below website and it states Carrier cats are generally not treated. As long as fleas are controlled, a carrier cat is not contagious.
It also says that cats generally respond well and quickly to treatment, so I hope your foster will be just fine.

Here is a link that might be useful: Feline Infectious Anemia

Thanks Petra

I saw this website, and unfortunately, have been getting different opinions. While the cat appears fine, the shelter had to send her back, since as a carrier, she cannot be adopted out through them. The shelter vet suggested that the cat would potentially go through bouts of the disease on and off, as the parasite is never eradicated.

I will continue fostering her, watching for sings of anemia (she has gotten anemic in the past), and hoping for the best...