Fes2K6

Hello My wife does not work but claims child benefit for one child. She earns interest from savings. Am i correct in assuming she can earn a maximum of £17,570 a year in interest payments without paying any tax? Also, if them interest payments are above £10,000 a year, she would have to fill in a self-assessment? It's all a bit confusing. I'd appreciate clarity on the above. Thanks very much