What happens when the club leader no longer meets the requirements?

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.

I was hoping to transfer leadership to her brother, Stetson, but the closest option is for her to completely resign from the club. I don't want that though. So hoe do I transfer leadership?

"PenguinFoop;c-18050132" wrote:
I was hoping to transfer leadership to her brother, Stetson, but the closest option is for her to completely resign from the club. I don't want that though. So hoe do I transfer leadership?

Select Stetson as the sim you are controlling and have him interact with her. Select the option from the "club" category of the social menu requesting her to step down. Leadership passes to the sim who makes the request when you succeed with that interaction but the former leader remains in the club.

I've never had request to step down fail when a relationship is good between the club leader and the sim making the request. I assume Stetson has a good relationship with his sister already; if not you may have to build it up a little before the request will succeed.

Yeah they have a great relationship. I did that in a different game though and the person who was the original leader took it hard. I don't remember for how long though and she had the leader of the pack trait so that didn't help.
I was hoping there was a way for her to voluntarily do it. Is there no way?

"PenguinFoop;c-18050157" wrote:

I was hoping there was a way for her to voluntarily do it. Is there no way?

Not that I'm aware of, which is a little silly, but it is what it is.
The only negative effect is a Sad Moodlet they get for not being the leader any longer, but it's not a massive negative, only -2 iirc, which is super easy to just completely ignore by having a few positive moodlets in effect before you do it. I

If you aren't able to get enough positive moods so that you can just ignore the sad, then just have her go to a computer and blog about feelings to rapidly diminish the duration of the sadness. It will get rid of it very quickly.
Jogging to clear mind, writing in a journal or giving herself a pep talk in the mirror all also rapidly reduce sadness duration if she doesn't have access to a computer.

Good suggestions. She's in a moody phase now though so sad seems to be her new happy so I'll hold off and see if she gets over it. I don't want her any more sad than she already is!