Poetry competitions for 12 year olds

I don't know of any but a word of warning. Some companies run competitions and the prize is to have your poem published. Of course the parents, grandparents etc buy the book at an extortionate price and receive a cheap booklet. Every child 'wins' although the blurb doesn't so this. It's a scam to sell the cheap booklets at a high price.

www.writersreign.co.uk/young%20writers.htm
Her school will get details of lots of local and national competitions. If you Google, then you can hind details. If your library is open, often they will have information about competitions.