The Betta MIGHT be okay in there. It's worth a shot. Let me give you examples of why I say might:
I present you with two female Bettas to take into consideration: Snow White & Pixie.
Snow White (Snow) lives fine with other female Bettas. She doesn't hassle them, they don't hassle her. She lives with four other female Bettas and two Croaking Gouramis. But she HATES Guppies. She was in a Guppy tank less than two seconds before reaching over and performing a tail-ectomy on my pretty male Guppy.
Pixie, however, hates female Bettas. She can't live with them, even in large numbers, because she ALWAYS attempts to kill them. She hates the Gouramis just as much. She thought the male Guppies attempts to mate with her were annoying, and, after putting up with him the first couple times, she flared really big and scared the crap out of him. Now, every time she comes by, he swims away as fast as he can. Everybody is happy. She likes the female Guppies. She likes the Mollies.
So, you see, they really can go either way. The only way to know what a Betta is going to do is to give it a try.
