He very carefully and politely examines her, making sure to explain what he's doing at each step (and pausing to make an improvised stethoscope.)

She's in pretty good health, all things considered, other than the malnourishment, but she has scabies and impetigo and head lice.

...She also wants to know EVERYTHING. Why is he doing that. What does that tube thing do. What is he finding out about her. How is head lice different from other kinds of lice.

... He really can't wait until he works out antibiotics. Aggressive hygiene and seeing if prestidigitation can wash things hot will help, but the lack of antibiotics and endecticides is going to bother him.

And he's very happy to explain!

He's using this tube to listen to her heart and lungs to make sure they're working right! Does she want to try using to listen to his heart to see how it works?

He has grave news. He has found out that she is... A child. It may take years to cure, he's very sorry. (... She's also obviously a street kid living in crowded conditions and with poor access to water to wash in, but she already knew that and he can't really make kid friendly jokes about it.)

Did she know that every type of (... She isn't going to know what a mammal is, is she) furry creature has its own kind of lice? Those lice can only live on the kind of creature. Humans are special: they have two kinds of lice.

Whoa!!!

What does a heart do? Why does it go thud-thud like that?

A heart moves blood around your body! Your blood contains lots of things your body needs, and the heart helps it get everywhere, from the top of your heard to the tips of your toes.

It goes thud-thud because it's squeezing and un-squeezing to move the blood around.

Imelda wants to know what ALL the body parts inside her do, actually. 

Well, along with her heart, she's got her lungs which take in the things from the air she needs, and gets rid of the things she doesn't. And she's got kidneys for keeping her blood clean and making sure she has the right levels of salt and water. And she's got a liver...

:O

This is the face of someone who has just discovered the concept of knowing things and would now like all of the knowledge immediately. 

"...Bun, can I have a minute?"

But he's got such an attentive and excited student here! Tanidio can have a minute.

Outside the room:

"I cast Detect Thoughts on her and she's very smart. Smarter than you, probably smarter than me."

"... That sounds very plausible."

"I don't know what you'd want to do with that, just, thought you should know."

Back into the room. 

"I want to be a doctor!" Imelda announces.

Look, this is just a ten-ish year old saying things. They do that.

But also, if he wants to improve medicine in this world, he does need smarter people who will out live him working on The Project. "It's a fine ambition."

"Can I be your apprentice? I'll work really hard and sweep the floors and chop up herbs and boil water and everything!"

"If Tanidio is okay with it."

Pulls Bun aside:

"You realize she's just doing this for food?"

"There's a sense in which I'm a doctor for food."

...he can't actually think of a way to argue with that. 

"Doctor! How are you going to cure my sickness? Are you going to pray to Asmodeus?"

"...sulfur and washing, actually."

He yells for the nearest halfling and tells them to bring water.