I’m sorry you’re going through this with your kitty. It’s not a fun illness to get through, but if you’re successfully syringe-feeding then you’re 2/3 of the way there. It can definitely take 6 weeks or more to get her back to normal.
Some tricks I’ve seen used in the past (all with different cats, as our feline friends are certainly persnickety):
sprinkle a little catnip on the offering
sprinkle some FortiFlora on the offering (you’ve already tried)
smear a teaspoon of meat-only baby food on top
make sure the offering is warmed up a little
fancy feast all-fish stuff, especially the sardine heads and pieces in aspic
junk-food kibble (Friskies), or even that semi-moist stuff
human-grade canned tuna
anything off your plate
Even licking a little off the top is a start!
Has your vet prescribed any cyproheptadine or mirtazapine as appetite stimulants? Is your cat on Denosyl?
Did your vet make any other suggestions such as a feeding tube (either nasal or surgically placed through the esophagus)? Sometimes they’re not necessary if the cat is easy to syringe feed, but the syringe feeding can put them off the thought of eating on their own. I’ve seen cats not eat on their own until a feeding tube is placed and they’re not force-fed for a couple of days.
Offer the food to eat before every force-feeding, before you’re getting the force-feed stuff ready, so the cat’s not associating them.
Keep the food offerings to the feeding times. If you normally leave kibble out for free feeding, take it up so you know she’s not nibbling when you’re not looking.
In the future, if you normally have fed kibble and want to continue, make sure you’re meal-feeding a measured amount twice a day so you know she’s eating and how well. I meal feed my three cats their kibble, so whenever I put it down they’re hungry enough to go to their bowls right away and I’ll know if anyone’s off their food. Keeps them from overeating, too.
Sounds like you’re trudging through, try to keep your spirits up, and best of luck. Hope this lasts for as little time as possible for you.