If she has gained weight it very well could be her own issue with her body...this is something she has to come to grips with. What about buying her a nightie of some type, that's a light fabric, so you can feel her through it, but that gives her enough coverage so that she's not self concious?
I just recently bought myself two nightshirts....they are a very soft lightweight t-shirt fabric, but with lace around the neck...so a bit feminine and pretty too. My H comments on how much he likes these on me....why? Cause they cling to the right spots I can sleep in these because I don't get warm in them (very rare for me). I've started wearing something on occassion to bed simply because of our S.
My thinking in this suggestion is that...it might at the very least provide you with some of what you want, nope not bare skin....but as thin as these are it doesn't inhibit you touching her or feeling anything either....yet it might help ease some of her body image aingst too.