G.B.
I think you could ask different plan providers about the situation. We have a family plan and it is expensive but we have everything.
I think go phones are nuts. If they use the phone there is a charge for the day, then per minute, then for all kinds of other stuff. It can be $25 for just one use. My friend had one and she got stranded and had to use it. The fees and add on stuff really added up quickly. It was a page long bill just on that one situation.
I would try to find a different plan and keep her on yours. For $10 per month plus some extra too you know she has a back up plan if needed. Since she is working can she pay for it herself?