I think using your left signal if you're leaving on the third exit of a four exit roundabout is actually standard practice in some countries. I saw people do this a lot in Norway for instance.

As a European it's very cute listening to you guys working out how to signal on a roundabout.

But to give some help... Signal as if you're going to continue round until you pass the exit before the one you need at which point signal for the exit.

Yeah your mom is right. An entrance signal is useful on smaller roundabouts, but is always less important than the exit right signal