After the last two weeks, I am done. How to tell her?

[StrongDadOf2]

She went into "survival mode" (her term) for the two weeks that my parents visited over spring break.  Catatonic at meals, completely minimizing anything fun my parents did with the kids, waking up ungodly early to go to work, going to bed at 7:30pm to avoid everyone.  It was like a ghost in the house that left dirty dishes around.  She cornered me in the bedroom to yell at me over a landscaping project my dad and I were completing; that was rather scary, but I got out of it without getting hit this time.  I bought my son (S11) a new bike, and the only thing she said when he excitedly showed her was, "Go put it in the basement."  Refused to let me be in Easter pictures with the kids, because I "don't think that sunrise service is special enough."  No clue where she got that from.  In couples therapy, when I told her that I felt hurt by this, it didn't even register with her.

Now that my parents have left, she's manic.  I swear butterflies are going to shoot out her butt at any minute.  She's back to shielding me from our daughter (D3) and planning complex events. Her: Why not bike to the bus and take the subway to bike to the toddler's concert and back.  6 hours of public transit for a one hour kid's concert will be an epic adventure!  I can drive them to the subway and it'll take less than half the time.  Her:I know you think it's crazy, but that's what makes it fun!

I've got a lot of paperwork done to retain the lawyer now.  What I think I need help with here is How do I break it to her that the marriage is over?  I'm fairly sure she won't expect it, even though she threatens it a few times a year.  She's been making some long term plans lately, so that bodes well for her not to be on the suicidal end right now.