I actually think Michelle was gunning for Dan as well.
Either way, with Dan breaking his deal, Ollie would have been gunning for him, and I think we both agree there. However, we must remember Michelle is, well, a very bitter person with an unrequited affection for a certain muscle-laden man-child named Jessie. Jessie went home on a 4-3 upset vote that hinged on America's Choice: Dan. She has been seen to be very bitter about that.
Additionally, even though Keesha and Libra were her nominees at her HOH, Dan was the next one to go up should one of them be taken off. Neither were, so it didn't matter, but it's hard to find a reason why Michelle would change that. Memphis is still a quasi-friend, Renny and her haven't had problems, the other two are in her alliance, leaves Keesha and Dan. There was also talk that Ollie and Michelle were planning to put up Dan. If he analyzed this correctly, he sees Michelle as a threat to his game and the biggest physical threat remaining (She has memory and physical skills).
I think Michelle would have been mad if either she or Ollie went up, maybe it's just different degrees.
The alliance paths actually make sense if you look from their bizarre, short-term memory way of it. Mind you, this isn't logical, just how they are. They are messed up
Part of the Jessie-Angie-Memphis team to begin with.
-Angie gets booted by a Keesha led HOH (-Keesha)
-Jessie gets booted by an April led HOH, but by a Keesha-Libra-Dan-Renny executed plan (+April, +Ollie, and +Jerry for trying to keep Jessie, -Keesha, -Libra, -Dan for getting rid of Jessie, since she'd be turning against everyone if she shunned April for putting him up)
-Memphis lands on Keesha's side as she fills in for Angie in his alliance, so Michelle is out.
I know you don't want me to get started on Keesha, and this is going to sound nuts but...she's possibly played the most logical game of all these boneheads. It's kind of crazy.