Could not find any info using the given Model Number. Tried here and GE.
Please check it.

Remove the back panel in the freezer and check the evaporator coils.
If they are heavily iced up then you have a defrost problem.
Defrost system consists of:
A defrost heater. GE likes to use a glass type heater on many units. They go fairly often. Should have continuity. Sometimes you can see where it has burned out.

A defrost thermostat. This shuts the heater off when all the ice is gone from the evaporator coils. It should be closed (0 ohms) when frozen.
Sometimes you can see that it has bulged and needs replacing

A defrost timer. Some units use a mechanical timer, some have an adaptive defrost board and some run off the main control board.

Best to check the heater and the thermostat with a meter using ohms.
Also use a meter to check if the above are getting voltage.
Does hubby have a meter?

Here are a couple good sites with basic refrigerator repair info.
http://www.applianceaid.com/refrigerator.html
Refrigerator Repair Guide: How To Fix a Refrigerator - ACME HOW TO.com

Here is the parts breakdown
Replacement parts for GE TFX25ZPBEWW | AppliancePartsPros.com

Fresh Food section Item 257 is the defrost timer
Freezer section Item 230 is the heater and Item 240 is the thermostat

Finding wiring diagrams for GE is difficult. Check behind the front kick plate or the rear bottom cover, it may be there.

There is usually an access hole to the timer's cam. Rotate the cam till the compressor and fan go off. You are now in defrost mode and the heater should heat up as long as the thermostat is frozen. If it does then you need a new timer. If not it is either the thermostat or the heater. Also could be that the timer contacts are not closing but this is uncommon. Best to use a meter.