Had a few mins with my coffee to look at this in Lr. In a properly exposed image the histogram will reflect data stretching from left to right (black to white) with shadows, and mid tones represented in the middle. Blacks and shadows are what create the contrast in the image. In a High Key most of the tonal range is pushed up into the lighter tones (the highlights), but that doesn't mean blow out the highlights, or delete the shadows and blacks, you still need "all" the data. IE:

Note there isn't much data in the blacks and shadows, but it still has some, all way from left to right.
Now, by comparison, here's the histogram from the OP
See the difference? You fell short on the left and right, resulting in an image without white or black.
Now lets look at your image. The first thing I note is what should be black, what should be white, and adjust accordingly. Now look what happens when we modify your image more like the first histogram example.

There's data all the way to the left reflecting the black I saw in the image, there's very little mid tone, which is what I'd expect to see in high key, and a lot of data loading up in the highlights. I know I've reached white, because I'm all the way to the right. Note also that the white is not blown, you don't gain anything when you blow the whites, and it's a lazy approach in a high key. Now here is the revised image.
I didn't touch the contrast or exposure setting. I did a radial filter to isolate the face and raise the exposure slightly on everything else in the image, and an adjustment brush to sharpen the eyes, and nose. Where most of the transformation took place was in the Highlights, Whites, and Blacks. With some minor adjustments to Texture, Clarity, and Dehaze. The Dehaze slider can work both ways for you. It can clear a hazy sky, but it can also add an element of haze to an image.
The only contrast adjustment was in the mild s curve.
