Female Betta

I would leave her on her own. Bettas, including females, are solitary fish which don't need company of their own kind.

It is possible to keep several females but they are usually kept in a tank with no other fish except perhaps some cories. This is called a sorority, and there must be a minimum of 4 females, with more being better. They are still fighting fish and have been bred for aggression for centuries. With several females, this aggression is spread out and no one fish gets picked on all the time. But even then, you could end up with a particularly aggressive female that will attack all the others.

No. Bettas and gouramis should never be kept together.

Both bettas and gouramis are territorial fish and occupy the same area of the tank. They are closely related and will see each other as rivals. While females of both species tend to be less territorial than males, bettas have been bred for hundreds of years in the far east as fighting fish. They have been selectively bred for aggression. Just because they have been bred for colour and fin shape for the last few decades does not mean that the aggressive genes have been bred out of them. And females of some species of gourami are almost as aggressive as males - this is most noticeable in the colour varieties of three spot gouramis (blue, gold, opaline etc)

There is, of course, the option to set up a small tank (something like 25 litres) for the betta, then get some honey gouramis ...............