I agree, free choice hay in the winter and no stall time. Blanket her if she doesn't grow enough coat, but leave her nekked if she's nice and furry.
She is still chubby, but not bad. I would ride her more to help build topline and bring her belly up. If you're not riding her, lunge her with side reins at the walk and trot, with just a few laps of canter each way. I'd rather have my horses be a bit chubby going in to winter than thin. I think she'll be just fine.