I'd say Michelle was symptomatic, not causal. The fact there was legitimate racism (ironically more from the 'white saviors ' on the left) which was aimed towards her specifically... didn't help.
In fact, lets talk about this because I don't think anyone here has. Michelle was and is a strong personality to the point that many joked about her being the one to wear the pants in the relationship and more than a few jokes cropping up of "she's actually a man". Now, I know for a fact this woman wanted to do more than just be a pretty face to smile at the camera. She trailed through Wisconsin a few times to push her few initiatives and she -really did- push them. Some even were -beginning- to get some groundswell support.
And then the Democrats kneecapped them. Not Republicans, the Democrats.
You see, I got a front row seat due to working out of Washington at the time to see as the Democrats informed her over a few months that she was to sit down, shut up, smile at the camera, and not do anything too strenuous. While the stated reasons were never revealed outright, the word at the time was that the very white Democrats were afraid Michelle would go full "African woman stereotype" and ruin their tailored image of Barack. When she fought back against the frankly ridiculous idea... she was forced to heel.
It's the bigotry of low expectations rolled into some outright racism. Which combined alongside the Birther thing and your own notes of getting high on her own supply.... well, it's not shocking she'd come out of that with a dislike of white people in general.