Hi Nomad, I am so sorry you are experiencing this difficulty. You did well getting off the phone when your daughter screamed at you.
She is in the wrong: you do not owe her to pay for any schooling as she is an adult . You have already helped a lot (didn't you say you bought this condo for her?) and she does not seem to have gratitude for that .
Please don't take this the wrong way as I understand why you did it , but offering to pay her for volunteering was a mistake. It triggered her entitlement. My daughter acts similarly when I have asked her to take over for me in my business, not wanting to accept my pay rate and demanding my rate when I am the business owner and get to determine her rate.
I would redact my offer to pay her anything for the volunteer work due to her screaming at you. I would simply say I have changed my mind and the deal is off. You don't owe any kind of explanation.
You feel good when she does well and feel bad when she doesn't or acts out . I did this for years and an finally learning to have more emotional balance regardless of what happens outside of me. It's about taking care of myself , tending to myself and my needs that has brought me a little bit more out of that pattern. We want our children to do well for themselves but we can't force it and I can't let it be the basis for my feeling well or being happy .