Mira is a bit taken with herself. Suffice it to say, she’s never looked that good in her life.
I’m borrowing a page from John Scalzi. I’m not going to explain what page I’m borrowing. Figure it out, and read everything he’s written to do it. It’s worth it.
The page I’m borrowing makes perfect sense, in context. It’s not that Mira doesn’t look like she did before, excluding the fact that she was 51 years old 31 years ago and she doesn’t look it all. (Imagine she looks about 20. I know she looks 12, that’s the anime influence, and the hair/make-up. I’ve noted this before.) She recognizes herself as herself. It’s just very close to her ideal self.
Here, we also have the most obvious example of the fact that this world is not the present. You generally can’t talk to mirrors and make them change their reflection properties. I expect we’ll have that technology on the market in the next 10 years or less. We can, IIRC, do that today, if we wanted. I think somebody did a phone whose screen could make a fair go at it. In this case, I imagine that glass is basically a pair of panes with a layer of nanopartical e-paper between them. Probably several layers. The layers can interact to form all sorts of images and surface treatments, including “Mirror.”
Up to now, all of the reflective surfaces in the room have been in frosted mode or too small/far away for Mira to have an idea of what she looks like. She knew she’d changed, but not how much. If she seems to be taking this all very well, it’s because she’s a very cynical person. Also, she has issues. She deals with her issues by doing her best to appear as if she doesn’t have issues. From a medical perspective, if you had the technology to restore the dead to life–that is, the technology to heal extreme levels of injury–Mira would be way down near the bottom of the people you’d use it on. Not as far down as Nero or Hitler, but pretty far down. You’ll see why later, but it’s related to her issues.
MIRA: What exactly did the surgeon do?
DOCTOR: You were rebuilt from the DNA, out. It was necessary to meet the terms of your contract.
MIRA: What does that mean? In people language?
DOCTOR: Let's put it this way: You're fifty-one, right?
DOCTOR: Have a look. Glass. Mirror: Full gloss.
MIRA: I'm... Beautiful?
DOCTOR: Don't let it go to your head.