From what I remember it doesn't effect her lifespan. For those that have abilities getting tired afterward is normal. Asher mentioned that a couple chapters back. The MC is more limited in her use of her ability and gets tired quicker then Asher does because she is more "removed from the source" of the ability then he is. This will be explained later in the story once she tells Asher about her ability.
Oh okay thank you. But why did she grow so quickly then? Or is it unrelated?
She's already knows how to act "grown up" from her previous life so she can give off the right aura even though she's only mid-teens.
Oki thxx
For those who read the novel, does the hourglass take her lifespan off, or is it giving her borrowed time, as in she'll inky live up to the age she died at previously?