> But if it's true that natural immunity + vaccination) is stronger than vaccination alone, is it worth it to leave her unvaccinated against Covid, at least for now, in order to get some natural immunity

No? If she does not get infected after vaccination the job is done. The goal is not 'theoretical maximum protection' the job is 'not getting sick'.

If she gets infected after vaccination (very possible), she will have less risk during infection and have improved protection after.

Vaccination first and then infection is definitely safer than the other way around.

Ofc the risk for young children is low either way, so going with the low risk of being unvaccinated might be something you are ok with.

But getting infected to get best protection against infection is kinda backwards.