I don't know that this is so much an 'emotional issue' as much as a learned response. It sounds as though a habit has developed. My daughter went through just the same thing, and because of some extenuating circumstances on her end, I let it go on for a while. But it got to be overwhelming (sounds like that's where you are), so I started reining her in, gently.
When she flipped out, I would have her sit on the steps until she could be calm. Once she was calm, I'd give her attention and snuggle her and talk her through her frustration. Right now, your daughter knows that when she flips out, you're going to coddle her. If you can keep it together and refocus her on a more appropriate method of expressing her emotions, she'll be far less unstable. It takes a while; habits are hard to break. And be sure to explain when tears are appropriate, when it is ok to yell and scream, etc. and really, really heap on the rewards for proper behavior.
Yes, you want to acknowledge the emotions under the behavior, because they are (usually) rooted in reality. She may be disappointed about the socks! But her reaction is over-the-top, and you can help her understand what is appropriate, and now is the time, before this becomes who she is.
IMO, I think kids are way over-diagnosed these days; it seems that anything other than picture-perfect behavior is seen as a syndrome or disorder. Not that there are not sensory disorders, etc., but the waters are getting muddied. Try some good, old-fashined modeling and re-directing, some limit-setting and rewarding good behavior, and I bet you'll see a significant change for the better. If you don't see improvement after consistently (there's the key) working with her after a few months, she may have a bonafide issue...but don't jump to conclusions too soon.