"accy queen" means the accy queen is a woman who rules the accumulator game — the one in the friend group whose football knowledge and betting instincts consistently embarrass the lads who thought they had the market cornered. It is one of many casual words teens pick up from friends, social media, music or sport, and on its own it carries no particular warning. If you hear your teen use it, it is fair to ask what they mean by it in their friend group, since meanings drift quickly. Asking out of curiosity rather than alarm tends to keep the conversation open and useful.