"Glow Up" - have you heard this phrase before?

Gonna give all the Glown Ups here a chance to see Sophia in a TV news report released today, talking about the San Antonio Food Bank:

http://www.twcnews.com/tx/san-antonio/giving-back/2016/08/24/high-school-freshman-propels-san-antonio-food-bank-to-new-heights.html

Her mother is in the green shirt. I am not there.

That reminds me of “blossomed” in the sense of a gawky/young teen becoming a more mature, attractive teen – but does “blossomed” mostly refer to breasts/curves getting bigger/“filling out”?

I’ve heard it like that, and I’ve heard it more neutral sounding. When it’s said in that euphemistic way it means what you described. But I’ve heard it also in the context of a shier girl opening up, or a tomboy starting to dress pretty. So it can’t just mean that.