Sloshing liquid sound, can hear when driving

Do we need a new heater core? I can hear a sloshing liquid sound while driving my daughters car, whenever turning there is a sound of alot of liquid moving.

could be a plugged evaporator housing drain tube

I can’t tell you for sure where the noise is coming from, but you do need to find out and have it fixed. It could be very cheap or medium expensive. I an thinking it is cheap (See love-car-talk’s response)

Is the radiator full? Sounds like it might be low.

The car is probably low on coolant. The noise you hear is coolant and air bubbles gurgling through the heater core. First thing to do is to top off the coolant and get the air out. Then, check the coolant level periodically, like every day, to see if there is a leak.