I called the phone company and we can actually save money on separate plans so that is the approach I will take.
That sounds like a really good way to play it, I think it would come across well from that point of view. If you are still happy to pay for the other things then you should, although maybe you could ask for a small contribution just so she has to put something in. Or maybe that is a little petty, go with whatever you feel is right for you.
