It's not just the legality or safety that she should consider. I mean - when they're facing forwards in their seat, they are sitting upright and well, that can't be that comfortable for a not quite 4 month old could it?

I didn't turn my bub around until he was 7 months as I waited until he reach the recommended weight requirement to turn him around. Likewise if you have a bub who is bigger (than average) I would wait until they reached the recommended age befure turning them around.

If she's worried about not seeing bubs, she can buy a fisher price mirror that goes onto the back of the seat. It keeps him entertained, plus you can then use your rearvision mirror to see what he's up to.