Recovery from hip operation - what's correct height of raised toilet seat?

My Mom is in hospital having a hip operation and I will be looking after her when she comes out.

I need to get her a raised toilet seat but not sure of the correct height to get. She is 5 foot 2 inches so should I go for the 2" or 4"? I'm thinking probably 4 but not sure.

Have left it to the last minute so be grateful for comments from anyone who has been in a similar situation?

Thanks