A 30-year-old friend is giving you flashbacks to high school. She's overly dramatic, jealous, out of control and a total energy drain. Is it worth trying to save the friendship, or is she like a bad high school boyfriend who just needs to be dumped? Miriam's Advice Well has a purpose-filled flashback.
Your friend is giving you flashbacks to high school because her maturity level rivals that of someone half her age, and at this point in your life, any social situation that reminds you of high school, and not in an ironic kind of way, seems like something to avoid. If she were "just" dramatic and jealous, you may be able to laugh it off and still have a good time with her during her good moments, but if she's draining your energy, too, then her actions aren't just self-destructive, they're destructive to others (specifically, you!) as well, and it's hard to imagine why you'd put yourself through that.
If most of your socializing is with friends from high school, then perhaps she comes along with the pack. In that case, you may not have much choice about seeing her if you want to keep your other friends, but a group of you who have known her for years may be able to intervene and help her grow up. You could try something like, "You seem really stressed out about a bunch of things that are pretty minor. We're here for you if you want to talk through something that's bothering you, but it's draining for us to have your issues be all we talk about every time we hang out." See how she responds, and then you can decide as a group whether you want to keep including her or not, and whether you can all work on changing the subject or ignoring her when the drama queen comes out.
If she's one of only a couple of people from high school who are still part of your circle, you may just be able to stop calling her and see if she gets the hint. In a couple months, you could try reconnecting and see if the pattern is the same and then decide how you want to handle the friendship for the long-term. On the one hand, it's heartwrenching to think about ending such a long-standing friendship. On the other hand, she doesn't sound like such a great friend, and it's actually surprisingly easy to distance yourself and make excuses and let the thing fizzle out. (Let that be a warning to you about friendships that you want to hold onto, too, though: it's easy to make a bad friendship go away, and it's sadly just as easy sometimes to let a good friendship dry up if you forget to put in a little bit of effort.)
On the off-chance that you're itching for a little high school drama yourself, you certainly have the option to stage a full-scale blow-out fight that ends with you dumping her as a friend. You'd get to tell her exactly what you think about her behavior, vent all your pent-up frustrations and give her the experience of being on the receving end of this craziness. This is decidedly not the high road, and I can't, in good conscience, actually recommend this approach. However, in the '90s movie version of your question where the friends stay together for years and are still reliving their prom as 30-somethings, the climax of the film definitely involves a screaming match, probably outside and in the rain. The movie likely ends with the friends getting back together, you with a little more appreciation of the fun in letting it all hang out, and your friend a little more mature and chagrined to see how badly she got used to acting. You may or may not get back together in the real life version, but you owe it yourself to see how your life moves on without her for now.