My 11 year old daughter started her period in december and has had it monthly. this cycle she has had her period for 12 days straight. its a light flow, but definitely blood and not brown or pink. are longer periods normal in the first year?

During the first-year menses can be irregular in frequency and flow. Egg release is inconsistent, and that function creates part of the hormonal balance of regularity. I would let her know this should normalize over time, manage as needed and get her on a daily iron containing vitamin. When she goes in for her next checkup discuss it with her doc or do so sooner if you wish.