So, I assume she is hooked up to AC at the campground.
If the AC heater in the fridge is working to keep the fridge cold, the check light should never come on since the fridge should be cooling fine on 120 VAC and the control panel should not be calling for the gas to light to cool the fridge.
If the fridge is cooling fine on AC and the check light is on, my thought is the control board has to be bad.
Turn OFF all power to the fridge AC AND DC (pull the 15 amp DC fuse and switch off the 120 VAC circuit breaker); wait 5 minutes; plug everything back in. Hopefully the control board resets and you are fine. Otherwise you may be looking at a new control board.
If the fridge is NOT cooling on 120VAC, then you have several problems at once.
1) CHECK for low DC power. DC is required to make this fridge work on AC or propane. The "Eyebrow" control board requires DC to run the fridge on AC or Propane. The LEDs will light as long as there is a minimum of 6 volts available to do so, but the propane valves and other processors/relays on the eyebrow board will not function to switch on the 120VAC heater.
Since "it works" the DC must be "OK"
2) Check for 120 VAC operation.
Does the fridge cool on 120 VAC? Turn off the propane and see if the fridge stays cool in "ON" - "AUTO". If it does not then check the breaker and the 2 amp fuse - then the electric heater. If it does, check the DC side.
One other thought
is possibly LOW 120 VAC voltage. Low voltage may not heat the ammonia hot enough to cool the fridge and the control board may be calling for propane assistance and the propane is off or bad. Check the incoming AC for bad power (less than 105 volts).
3) Check for propane operation.
Switch OFF the 120 VAC circuit breaker on the power center that controls the fridge. It may not be marked "fridge" as some campers are wired with the fridge on the same circuit as the microwave or kitchen wall outlets.
The fridge should soon call for heat from the propane. It will try to light the burner. If it does not, then the check light (which should come on momentarily and go out) will stay lit indicating (as F1100turbo said) the propane failed to light.
Possible problems here:
1) No (or no pressure) propane.
2) Control board failure
3) Solenoid valve failure
4) Wasp nest or bugs in chimney
5) clogged or damaged propane jet.