I don't know how much one needs in general and how much one might need to correct a deficiency. I really didn't do much research to be honest. It just seems like it should be quite easy to even correct a deficiency without using supplements as there is quite a number also otherwise very healthy foods containing lots of Vitamin A (kale for example, which one should eat a lot, especially raw :)). I think it's always better to get your nutrients/vitamins via food. But you should of course talk to her about that.