sibs

Hi gang I wonder if anyone can give me some advice? A friend of mine says her shower runs cold a few seconds after it warms up and she ends up having to pull the chord off and on again several times to get the water hot again which is not always successful. She thinks that it is due to low water pressure in the supply pipe and when the shower is turned on there is not enough water pressure and it trips out and runs cold. The shower is electric. Can low water pressure affect electric showers or is it more likely a fault with the element? She says it is an old shower unit.
I would really like to know what is going on here thanks!