Ok, first and most important things first: it's a cyst, not a tumor. My dad had a brain tumor that was found when it was at critical mass and almost killing him. It was a meningioma, and it was discovered on his 86th birthday and removed a week later. I know how scary something like this is. The decisions were up to me alone as Mom just couldn't handle it. It's overwhelming. You have to breathe and you have to have faith that you weren't given this amount of responsibility without also being given the wisdom to know how to handle it. Your daughter is lucky to have you for a dad. Follow her lead.
There is good news even when scary diagnosis hit: Dad renewed his driver's license on his birthday the next year. He celebrated his 91st bday in October. Ian, Dad's surgeon, saved Dad's life. Ironically, he also performed a similar surgery a year and a half ago on my lawyer's wife (we've been friends for 30 years, my lawyer, his wife and my family). If you feel like you want a second opinion, I can give you his name. He is a brilliant neurosurgeon at the Brigham here in Boston, but you are far away from needing that today and it sounds like your daughter's situation is serious but not as dire as Dad's was, thank God.
You can do this. You are not alone.
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Now for part two, WAW:
Honey I don't know how you could possibly feel anything other than angry at her response. It infuriates me to read her response. BUT: people often act one way when they are feeling something completely different.
I'm going to suggest something that I think will be incredibly hard, but necessary: let it go. drop it completely. say a prayer for her, because she needs it, badly.
You are by yourself with decisions about your daughters. It hurts me to write that because I don't want to be that blunt, but it's called for. She is not capable. It remains to be seen if it's an illness or a moral issue. The cause matters not as the result is the same.
Again, you can do this and in that you are not alone. We are here for you. Keeping all of you in my prayers, even WAW.
sending extra {{{{{{{hugs}}}}}}}
xoxoxoxoxo
PS let me know if you need the info on the doc
M 20+ T25+ S ~15.5 (BD) BD 4/6/15 D 12/23/16
"Someone I loved once gave me A box full of darkness. It took me years to understand, That this too, was a gift." ~ Mary Oliver