Oh God, this is unphantomable! Don't have Harley's Mama here but felt it could be genetic and her immune system is genetically and inherently weak. Now I don't know why her 3 counts are off the charts. But if I did I'd be keeping her isolated. The vet said if my other three have been exposed, its too late already? Harley is isolated in one room now. And I'm taking her to another vet for follow-up.
I'd have the other cats tested right away. As long as they're still negative, get those vaccinations and they should be ok. When I went through the nightmare with the 15 kitties, 2 were negative and managed to live through everything because they had the shots. Don't wait on those tests, for the other cats.......and for Harley. It doesn't sound like the test was done on her or they'd know if FLV was the problem.
I hope it's not FLV, that it's something that can be treated or that she can eventually outgrow. There's not much worse than the helpless feeling you get when dealing with that horrible disease. We can't explain anything to the poor lil critters. Wouldn't it be great to be like Dr. Doolittle? LOL!
I'll keep praying for Harley and your other kitties that things will turn out well. You know how much I adore cats, having 39 of the fuzzy "kids" running around here. :-)