"Hey kid! I got that 'medicine' you need for that affliction I definitely didn't cause. Sure, it's experimental and I have NO IDEA how it works, but it's mint, one of your favorite colors! Go on and test it-- err, drink it and feel better! ...come on, you can trust me; I'm a doctor!"

Come on, how can you argue with a face like that? She obviously knows what she's doing!
And, I'm pretty gullible and innocent and how the heck could my best friend lie to me?

On a more serious note, I know Di tends to have this devious look on her face, but she truly cares about her patients and wouldn't do anything harmful to them intentionally. She almost always looks like that and the sharp, shark-like teeth in her mouth doesn't really help when she's giving an innocent smile.
I do wonder what she does when she's alone... I mean, what doctors do you know that wear goggles? What would she need those for?
...
...oh boy.

This picture of Di exists because I was giving her a non-TF2-related outfit. That resulted in switching only a few things. It's hard for me to deviate too much... but, I need to for a reason... *coughcoughfurvillacoughcoughwheeze* So yay, normal labcoat! ...
.....
........
...sigh...

Di: Oh, you got a cough? I have something to test-- I mean, give you for that...
Me: NO!

I swear, Di treats like I'm some kind of lab cat or something... I mean, I thought we were friends... but all she does is use m--
Di: Hey kid, I have some candy for you!
Me: Really? Can I have it?
Di: Sure~ *gives*
Me: ...
Why is it glowing?
Di: It's chemiluminescent and definitely not radioactive! ⋅⋅⋅ʰᵒᵖᵉᶠᵘᶫᶫʸ, ᵗʰᶦˢ ᵗᶦᵐᵉ⋅⋅⋅
Me: WOW, THANKS! *eats*