First question: is my fondant gonna be fine when I roll it out or am I in for a disaster?
Second question: will my fondant make it another night in the fridge in the shape that I want it or should I roll it out and use it on her birthday?
It depends on your recipe, but I really don't see why it would not be absolutely fine. Normal marshmallow fondant doesn't need to be kept refridgerated, and it is harder to work with cold fondant, so I would take it out of the fridge and keep it somewhere dark at room temperature. As long as it is well wrapped to keep it from drying out, it should last a good long while.
I never put fondant in the fridge (unless it is on a cake) How long would a bag of marshmallows and a bag of PS last? They don't go bad. If your fondant is tightly wrapped and stored properly it will last quite a long time. Even if it dries out some you can knead a small amount of shortening into it.
I keep leftover pieces of mm fondant tightly wrapped in the fridge for months, to use if I just need a little of one color or another. Then just put small pieces in the microwave for 6 seconds at a time to warm it, if I don't have time to let it sit out to come back to room temp.
When I make a fresh batch I leave it tightly covered on the counter for a couple of days, at least overnight before I use it.