My daughter currently has a bath seat like this one and it's not working out no more because she…

We just switched to the regular tub and just don't plug the drain

I took my son out of it at 9 months too and started using the tub. We have a matt for bath tubs so he doesn't slip in case. He rather sit in it than sit on that thing away but they do have bath seats where they sit upright in it

if she sits up then just use the regular tub.

You can get one of those blow up tubs (there's a cute rubber ducky one) to put in the regular tub. It's will protect her from bumping her head and it's not too expensive.

Have you thought about putting her in a bumbo seat in the tub?

I would use the regular tub but if forever reason she gets upset she throws herself back and I don't wanna risk her hitting her head @abeals04 @andrewsmommy @ssdj4

they have mats to put in the tub so she doesn't slip. maybe put a small laundry basket in to keep her from flopping back @naenae

Have you thought about kitchen sinks that's what our grandparents did