Maybe, for a streaming event, she could measure her belly.
"How big are you now?"
You get out the tape measure to check. It looks like you're [number] inches around at your widest point.
Someone in the chat could also ask her to demonstrate her pregnancy walk.
You walk from one side of the room to the other, slightly exaggerating your pregnancy waddle for the camera.
(at a bigger size)
You walk slowly across the room, one hand on your swollen belly.
(next size)
You push yourself up from your computer chair and waddle around, one hand on your belly and the other on your lower back.
(next size)
You manage to hoist your enormous bulk out of the chair and stand, panting for a few seconds before you try a few careful steps. There's no need to exaggerate now. Your belly is so big it leaves you unbalanced.