Hi Satch,
I'm agreeing with what others have said here.
When I hit my bottom with my mom, I had to go NC for a few weeks - like 4, just to stop the constant churning and panic. After that it was about 4 months of very LC, and since then it's been LC (which for me is about 2-3 X/wk including texts/visits) (as opposed to several times a day, or 4-5 hours a day). If you are feeling ill, and feel like vomiting, it kind of sounds like you have reached your limit too, and you probably realize you need to start taking care of yourself.
You can't "fix" her or her problems right? Trying to do that, and "meet her needs" hasn't helped either of you. Time to take a new tactic, and live your own life, and let her live hers. She needs to do this to grow. Think of it this way: by bailing her out of her problems emotionally and financially you are enabling her to remain dependent on you. You are both trapped. Since you are the rational adult in the relationship (it is encumbant upon you to change the enabling, and allow her to find her own way. This is how she can grow. Don't explain this to her. Don't JADE.
It only makes things worse. She's trained you to feel guilty. You don't need to feel that. It's a process to let go of that guilt.
The more you are there to bail her out of her emotional and financial problems the more she will need you, and abuse you. It will only continue to escalate and get worse.
So, about setting "boundaries", do you think you could tell her you need a break from other people's problems, so that you can take care of yourself? Tell her that means no phone calls, no texts, etc for ___ weeks, or until you are well enough to contact her again (on
your terms). Make it clear that YOU will contact HER when you are ready. Then follow through with it. Like others have said, skip past/delete her phone messages (because she broke your boundary), block her on FB, your phone etc. so that you are truly NC. That is your boundary. You can't expect her to respect it if you break it yourself. Follow through is really important.
When she pushes back, tell her you need to go now, and you will contact her when you are feeling better, and hang up. Then go ahead and scream or have a good cry, or maybe a long long walk?
At the same time, start looking after your own health and focussing on YOU. Eat healthy, do some physical activity as appropriate, practice good sleep hygiene, look after appointments like hair/physio/massage/chiro/nails...whatever makes you feel better. Spend time with friends (but not talking about your sister) doing fun things. Also do things that are fulfilling to you in your spare time. Yoga? Karate? Meditation? Boxing? Prayer? Art? Sport? Netflix? Inotherwords, find your way back to living your own life, and not her drama.
This IS possible. It is also possible to let go of the guilt. It can get better.
Sounds like a good place to start is with "boundaries".