we assume the hourglass ages her, but there is no confirmation about its actual effects. its definitely forcing her growth but that doesn't necessarily mean aging in the sense of lifespan. there are still other possible effects it is having but we are all working on the assumption it moves a portion of her time forwards without the required time passing due to getting reset.
logically speaking, the power it would take to reverse time even by just 5 minutes, being powered by a person lifespan, should outright kill them after the first couple of flips if not the very first time. so the hourglass would have had a history as a cursed item before it reached her.
but its a story, so anything can happen as long as the author wills its, logic be damned xD