When you say the toilet isn't filling up with water, that could be the bowl itself or the tank.
If it's the tank, close the valve at the wall and remove either top or bottom connection of the hose between it and the tank. Place a bucket or pot under it and open the valve. If no water comes out - you found the cause. Check other cold water lines in that same bathroom to ensure water comes out. There's a blockage in the line and more often than not it's the valve that is blocked by debris. You or she might be able to clear the valve with some thin wire (like those twist ties off of bread loaves).
If water does comes out, and if it's at a high enough pressure...well, it's not like this is the first time a part failed in a new toilet. I've purchased new valves, electrical circuit breakers and GFCI's that didn't work right out of the box. So, she'll have to replace whatever failed in the tank (which is more than likely the fill valve assembly and they cost about $8 or so at home improvement stores).