I mean, obviously most people would rather their kid didn't need glasses, but... heartbroken? In shock? That seems like a very, very extreme and OTT reaction and I suspect your daughter has picked up on the way you feel, even if you think you're hiding it.
Her prescription really isn't that strong. She will look adorable in her glasses. Millions of kids wear glasses. It is fine and there is nothing to worry about. I get that it's a surprise to hear that your child needs glasses when you assumed their eyesight was fine, but it's really, really common for this to be the case.
FWIW, I was a teenager when I first got glasses, and I thought my eyesight was perfectly fine too. It was only when I actually put my new glasses on and saw the difference it made that I realised I'd basically been seeing the world through a fuzzy blur. Clearly, your daughter can see to read etc. But that doesn't mean she's seeing well. Better for her to have glasses than for her eyes (and brain) to be forced to make extra effort all the time.
I'm now 47 and I still have glasses - I don't need to wear them all the time, although I should wear them more often than I do, probably. Would I prefer to be able to see perfectly without them? Yes. Does wearing glasses actually have any real negative impact on my life? Absolutely not.