Please help.....advice needed!!!!

My son's snake Markey had a very slight upper respiratory infection. She went six weeks without eating. She was treated with Baytril and recovered from the infection but she still refused to eat. I purchased some ProBiotics from Kathy Love in an attempt to get Markey back on her regular eating schedule. For the last two plus weeks, Markey has continued to refuse to eat. I decided to try again today and my son held Markey while the mouse defrosted. All of a sudden the kids were screaming that Markey pooped all over Parker and the bed. I ran downstairs and sure enough, Markey pooped! I was told there wasn't any feces inside her....anyway, I was thrilled that something came out. I took a sample of it and put it in a Ziploc bag so the vet could test it.
I put Markey in the feeder cage and gave her the fuzzy (I purchased smaller food in the hopes that she would start eating again) dipped in the ProBiotic. SHE ATE IT!!!!!!!
The vet clinic told me to give her another fuzzy but I'm so afraid that she will regurgitate. I have her sitting in the cage and I'm wondering if I should offer one more fuzzy (she normally eats TWO large mice) or if I should wait a day or two to make sure this one stays down? I have never dealt with this issue.....
The vet clinic thinks she may have some sort of intestinal issue like Giardia but obviously won't know until the test the stool.
I want to feed Markey but I don't want to overdo it. ????
Thanks!