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If one side of the engine has low compression, then more than likely it is a blow head gasket. You can have a block test done which will test for engine combustion gases in the cooling system. Since the engine was running hot with a bad cooling fan, more than likely the head gasket was damaged. The cylinder heads are aluminum and the engine block is cast steel. Also, coolant getting into the cylinders will cause a hard start problem and a rough idle.
Yes, the converter turning red could very well be related. A bad miss fire or coolant in the exhaust will clog up the converter and also when her father added gas to it to keep it running, could have also damaged the converter.
I would have the testing done first. The block test is simple and nothing has to come apart but the radiator cap has to be removed.
Your welcome. I'll keep me fingers crossed for good luck for you.