"Hi!" comes a surprisingly cheerful voice from within that outlandish belly. A bulge that looks vaguely like a hand appears. You "shake" it. [More precisely you just put your hand on the bulge, but she seems to take it as a handshake.]

But that is a minor matter. There is something very strange here..
"There's just the one of you in there?" Surely not. There is room for an army in there. OK, maybe just a squad, but if Betty is alone in there, she could really rattle around.

"Right. All by myself."
"But..."
"Oh, we were playing shark."
"Shark?"
"Sure. You have a shark and a swimmer. Idea is for the swimmer to swim cross the pool without getting eaten. The shark girl gets some fins that let her swim way fast. Real easy for her to get to the swimmer. But she's only allowed to use her mouth to eat the swimmer.
"That makes it tough. You try to lunge under water and you push the water out of the way, and push the swimmer in the water away too. Not being able to grab or hold the girl is a real problem. You try to just lunge and you have to be very lucky to get a part of the swimmer you can keep hold of with your mouth.
"So the best tactic is to do it the way the fish do it. You make your stomach as big as possible and then you open your mouth wide as you can and suck in all the water you can. If you do it right the swimmer comes floating in too."

You turn to Shaska. Yes, that does explain some things. Now that you look, you see her belly is too smooth, and lacks the bumps that happen when several women are crowded inside. There is also some netting [the remains of her swimsuit?] holding the overloaded organ in a vaguely couch shape. "But how could you swallow that much water in one gulp?"

"Well, it was more than one..."
"Way more, to be exact" interjects Betty.
"Hush! Each time you swallow, you can eject most of the water, but some gets retained. So it can build up if you miss a couple of times."
"And Old Whale here missed me a whole lot. Got so full she could hardly move."

"Well, she did get you in the end."

"Oh no. I had to fish her out of the pool so she could dry out, and then I fed myself to her."

Now that sounds like the ultimate in good sportsmanship. The winner feeds the loser? "Isn't that rather hard on you?"
"Naw. All this water dilutes her acids something terrible. It's going to take her hours to digest me."
"But then?"
"You forgot what the nurse told you? That medicine you took means you can't digest anybody permanently. I'll just show up back in the nurse's office when I'm digested."

Hmm, perhaps you should get around to a visit to the nurse. But medicine always tastes bad...

"I do like to ask how they became vores. What was your 1st swallowing like?"

"Betty! That's really too personal a question for a 1st conversation."

You politely answer "Oh that's all right. I don't mind answering."