Yeah if the compressor clutch is cycling fast that is a very good sign it is low. Especially if the pressure readings back it up. Adding freon is a stop-gap as the system is supposed to be sealed - that means you have a leak and more will still leak out. If the leak rate is low, then it is the cheapest way to fix it (periodic recharge) but it isn't ideal.
That's why it is important to know all the key readings up front - low pressure side, high pressure side, ambient temp, and some idea of the clutch cycling rate and how cold the air is coming out the vents. Diagnosing without that info is more than a bit of a crapshoot. Based on the limited info you had from your relative, there was no way to really say it was low on freon.
Glad you got it fixed.