It sounds like you need to resync the transmitter and receiver again.
Does she have the instructions for the thermostat to do this?
Try this first;
What details do you have about the unit upstairs with the red light on?
Do you have the make and model?
Is this the TP9000?
This is not wireless, this is wired.
If the the top left hand light is on then the heating should be on - it sounds like this part is working correctly?
Do you have the make and model of the boiler?
Ok, just one thermostat?
The boiler is a combi - is it the heating not working or the hot water, or both?
ok, is she able to bleed the radiators upstairs to see if they are full of air?
what is the pressure gauge on the boiler reading?
Is there a TP9000 upstairs also?
ok if the boiler is on and the heating is on then normally a room thermostat would control another valve.
If you have no TP9000 upstairs then the whole system must work at once, the only thing it can be is air or the pump.
What happens if she turns off the downstairs radiators one at a time, does upstairs heat up?
If you look at the link I sent, the unit has a red light on when the heating or the hot water is on
So there is a thermostat upstairs?
Yes, this thermostat must control a valve.
If you can find the valve near the boiler then it might be stuck closed
If you find the valve then there will be a lever on the side or end enabling you to open it manually to get the heat back on