Whew, I just finished ALL the thread, and first to the OP, I'm sorry your DD is hurting. I think everyone has experienced rejection similarly, but to have it all at once from multiple sources IS brutal.
I loved the advice given about those sororities not rejecting the *real* girl, but rather who they perceived your DD to be in 3- 30 min "parties". Someone pointed out it's like speed dating and that's partly true too.
When I was in college at OU in the late 80's, Greek was beyond huge on campus. It was very much Greek or geek. I rushed and pledged a very popular house. I know the sting of rejection though b/c my first couple of choices cut me, but in the end here's my insight on what your daughter is missing out on: not a lot.

I had a 4.0 and was STILL forced to sit through mandatory study hall, my parents didn't have a lot of money and all I remember was dues, dues, dues. If it wasn't dues, it was "Here, go sell these balloons for $2 each and if you can't sell them all, you're buying them". It was a LOT of mandatory parties at frat houses. If you couldn't make it on a Tues night and you were on the calendar for that frat party, you had to find your own replacement to go in your place. Test the next day? Well, you better study early or find a girl who'd go in your place.
I remember lots of issues I had with being a pledge - house rules chafed me, it was shocking that "your" room wasn't really yours at all. There was one twin bed for two girls, so you had another bed on a sleeping porch.

Call me finicky, but I LIKE having a place of my own that I can always crash in without it being my night for the bed! Ick. Just writing this brings back memories I'd forgotten about!! Was it fun? Sometimes yes. I liked having a pack of girls (the pledges) that I could identify with in class or in the cafeteria. I liked the parties for the most part. I just hated having to ask my parents for more money ALL the time.
When I transferred to a smaller school midyear (living at home to save my parents money) I rushed again. Glutton for the rush process

I ended up pledging the SAME house, different school. Wow, I didn't do my homework because Greek life there was about 100x slower and less important than at OU. But they still had all the same rules and pecking order and mandatory stuff that just got in the way of my LIFE! I was working p/t, had a full time boyfriend so the frat parties were awkward, and living at home. I de-pledged about 6 weeks later. Best decision I ever made!!! I remember feeling so liberated telling the pledge captain I was leaving!
So, if that helps your DD in any way to read some of the parts of Greek life that aren't so pretty - - if she chafes in any way when people tell her what to do, when to do it, if she is turned off by how the girls actually schedule circles where a girl announces she's been "pinned" by a guy and girls are CRYING with glee, if she's in any way independent minded - - chances are she might have been less than thrilled with what the wizard of Oz held for her behind the green curtain.
And lastly, if she can take something else from this and learn to apply it to her dating life in the coming years? It's exactly what was said earlier; guys aren't rejecting her, esp after a few dates. They're sizing up what she's projecting or what they're interpreting as what she's projecting (sheesh..) and making a quick decision. Add to that the fickleness of youth! I wish my mom had prepared me more for the sting of dating and how to deal with that.
I hope your DD finds some comfort in the coming days and weeks. It will get better, and she will soon find other people and groups to fill her time. I'm sorry she's hurting right now.