I think she might be depress. could they see each other when they were seperated? are you finding her something different than she usually eat? you can try fasting her for a couple days until she eats again. I have a female betta and she seems to be a more picky eater than my male.

Maybe it doesn’t like the food.
Feed it a very different diet.
try pellets for 4 days.
flakes 1 day

& brine shrimp or bloodworms on saturdays & sundays,
im guessing

It sounds like it is “ick” and is most likely going to die soon. Once a fish starts behaving odly, there really isnt anything you can do to help it. She’s a gonner.

Its probably sick. I know when my fish started dying, it did not eat and it started acting weird. Give it a few days, making sure you feed it and see if it eats anything. If not, you might not have much more time with it. Sorry-hope everything works out tho. :]

A healthy betta eats, If she is not eating there is something wrong.
how old is she? Some betta get depressed I know I raise the darn things, I have one baby right now that keeps jumping and sticking to the side of the tank above the water, silly thing.. twice now he has done that.
You can try feeding her peas to see if she is maybe constipated, Sometimes that will bring them round. take a frozen pea,cook and skin it, and mash it to feed it to her, little bits at a time.

DO NOT CLICLK THAT LINK IN THE poster below me.. it contains a VIRUS

Well if the Beta Fish stops eating then it will eventually die of hunger.Or you can buy another one and put them together.