My mum uses Android. I have already used the electrum wallet myself and actually found it quite good. Updating the latest Blocks take some time if you not use it daily but that should be totally okay. Also I don't find that UI from electrum very nice.

A feature that I miss is that if my mum does a transaction that is over a certain amount, it would be a very cool if I could "co-sign" it.

So if it was your mum you would recommend electrum?

greetings!