Lots of great ideas - and also maybe it might be good to think longterm? seems that the root problem is an underdeveloped (and/or unconfident) sense of rhythm, so she may want to find a way of regularly working on this in an intuitive way, then she'll gradually start to get better at it and more confident herself, needing fewer props and help from others.

I don't really have the mechanics, so have to rely both on my own sense of rhythm and on really listening to what the guitarist (in my case) is doing to know when to come in, both at the song start and after an instrumental solo bit. Once you know the song really well, that'll come.

And using your body (rocking, tapping, swaying) to pick up rhythms really does help.

Might be worth even doing a hand-drumming class for a while, to learn about and get used to rhythms, both intuitively and mechanically. Don't worry about results, just "be" in the rhythms.

It's not just the brain that learns - the body does too, without us even realising it sometimes.

Sue