I'm only in the middle of Season 2, and I've already seen her put up with more than I ever would have. And that wedding fiasco would have been the absolute last straw for me.
Maybe I've just never experienced a love as strong as the two of them; maybe I'm just too stubborn and can't let go of a grudge. But boy, has she put up with a lot!
Again, I'm only in Season 2, so I don't know what happens later. But it says she stays through 2000...maybe the rest of her time with the show is merely as a friend rather than in a relationship with Charlie (hard to see happening, but we'll see)
While there was nothing wrong with the Kirsten character and she is utilized to perfection in certain seasons/episodes, I am in the minority that think she should have left the series long before it ended. The writing got a bit inconsistent and once that happened, they'd bring Kirsten back into the picture periodically and it just got old after awhile. The "wedding fiasco" was a perfect 'exit stage left' moment for the character.
Bringing Grace in for season 3 had tons of potential and there never would have been a need to bring Kirsten back ever again. Midway through the relationship, the writers turn her into this extremely unlikeable person and you know Kirsten is on the verge of coming back long before it actually happens. Of course she's back in season 4 and when we head into season 5 and the whole Daphne/Dianne thing happens and Kirsten is still there, it's just too much and drags down the quality of the show. The series was gonna end regardless as they were all entering adulthood and moving on, but the on/off friendship/relationship between Charlie and Kirsten would have been the nail in the coffin even if the show feasibly had a year or two left.