spoils--my first recording Thursday night messed up, so I couldn't watch until yesterday.
I think Kyle just snapped. Think back through the series, Kim is certainly not an "adult". There was one show early on where she kept going on and on about her "star" days, she sounded desperate when she kept going on and on. It got to the point where I felt painfully embarrassed for her. She's got this childlike quality where she acts on impulse and never considers the repercussions--like several times she said she wanted another baby and she really doesn't parent the ones she has, other than to want them close to her, constantly.
One of my biggest questions is where she gets her money. It was pretty much obvious that she and her parents blew their way through her acting money. I suspect that she lives on alimony and child support and ends up living beyond her means. The entire season, Kyle tried to gently nudge her into a less expensive home, cut expenses, and perhaps do something to earn money, but Kim blew her off. Then came the numerous times that she could have defended Kyle, but she simply ducked her head and said nothing. Kyle promised her mother, on the mother's deathbed, that she'd take care of Kim. A mother doesn't ask that unless there's a problem. Kim's a fragile Scarlett O'Hara/Blanche DuBois type: "I'll see to it tomorrow, tomorrow's another day"; "I shall depend on the kindness of strangers"; she's still a child and now evidently an alcoholic one.
I think that Kyle handled it wrong. She was always so gentle with Kim that Kim ignored it and flitted about on her merry way. I also believe the money situation with Kim is quite dire and she's an ostrich about it. That's when Kyle just let her have it. Unfortunately it came off as bullying and cruel, but at the end of it all, it was done in love.