Adult molts usually happen somewhere around 18 months or so (especially if you're talking about Spring babies) however as a chicken grows up there's a number of softer juvenile molts (where chicks transition into adult plumage), and yes on top of that sometimes younger birds can have an adult...
How old is she? Younger birds can still molt, which is what it looks like, as she has a good collection of pin feathers coming in. Are there other bare patches on her? (Edit: Just saw your other post, is the one in the snow the most recent? I saw some smaller bare looking areas on her back...