They should be automatically removed from the club when they age up and no longer meet the requirements. The leadership position should transfer to someone else that is in the club automatically as well. The club itself will still exist with all other eligible sims still members.
If you want to control who becomes the new leader though, I'd suggest transferring leadership before she gets kicked out due to aging up.
Note also that there can be a bit of glitchiness when the sim first becomes ineligible to be in the club, the booting-out and change of leadership don't always happen right away nor at the same time.
