Some females can just be too old to mate, too, and therefor are nasty-tempered and more interested in shredding your fish than mating him. I've had a female like that before. I only knew she was a girl because she'd sometimes show vertical stripes when she was younger... but she'd never breed. Frustrating!! >.<
I can't imagine how angry I'd be if I was sold a plakat male as a female betta... but I guess it's easier to make that mistake now that females look so much like short-finned males....
Anywho, back to the subject!!
Male and female betta in a 10 gallon? Please don't even risk it.
Not unless you have a backup plan to set up a separate tank for her. If you want your male betta to have companions, add some rasboras or pygmy cories or a snail instead. He'll chase them a bit until he gets bored of it and then he'll probably leave them alone. Better than him spazzing and killing a female betta or her spazzing and shredding him, right?