If she doesn't have another job, just make her your partner and pay her half. As a partner she doesn't actually have to work, she owns half and takes half. Then you get double the tax free allowance (about 5k) so that makes about 10k of your earnings tax free!
My wife actually does work with me, but she would still be my partner if she didn't. You fill in one partnership return, and a personal return each, but the're easy. No one works for anyone, you're both equal, no one has to pay employee insurance or employee NI contributions. You just take half profit each.