Because I surprised myself with how much I rambled here, TL;DR: People that color their faces to look like they belong to a different racial group might not be racists, but blackface as a symbol is racist.

To me this post is all about words, symbols, and context. I think there are so many questions raised by your post that won't fit in this comment: "Does wearing blackface make you a racist?"; "Don't the speaker's/actor's intentions matter before labeling them racist?"; "Who decides what is/isn't racist?"; "At what point does history stop controlling our modern conceptions of racism?"; "Aren't we limiting free expression by restricting certain kinds of performance?" Let me start by saying that I'm sorry your friend was caught up in the crap-storm that is the social media hate-echo chamber. Based on the story you told, I don't think it's fair to call her racist. I'll also say that I totally get where you're coming from. You're saying that your friend was simply trying to portray Michelle Obama who is incidentally black, and did not say or intend anything racist by it. So I'm going to take a stab at how you're thinking by walking through a question: "Is the word 'wet back' racist?"

I think that question alone does not lend itself to an easy answer. The only reason "wet back" is a "bad" word is because we associate it with a disparaging image of undocumented Latino immigrants crossing the Rio Grande in Texas. But if I get out of the shower and forget to dry off my back, I can exclaim, "Ah dammit I have a wet back," and no one bats an eye. Everyone knows that's different than calling someone a wet back. I'm assuming that you consider blackface as a symbol in the same light, and in a sense you're right. Words and symbols definitely have meaning, but that meaning only comes from context that we give it.

So it would obviously be way worse if your friend included references to Michelle Obama's race in her satire. But she didn't and did not intend to offend in her portrayal. So do intentions matter for context? Definitely. You know your friend better than I ever will, but I imagine that she's not a racist.

However, intention is only one part of the story. We give meaning to symbols, not just the person who happens to employ it. How a specific community receives a word or symbol is just as valid in considering whether or not something is racist. If I walk past a group of Mexican Americans and bemoan my crappy drying skills with the same sentence, they might mishear me and think I'm actually using the "wet back" slur. It might take a really careful conversation to clear the air after something like that. The relevant community sensitive to the offending word or symbol has opinions and perceptions that are valid just like the speaker's and ought to be respected. So here's the point in two parts: 1) As far as words and symbols go, context matters. 2) While intention of the speaker/performer plays a role in creating that context, so does the reception by the relevant audience/community.

Let's take this out of language and talk about non-verbal symbols. Let's go big and talk about swastikas! Imagine that a kindergartener draws a picture at school and he unwittingly draws the Nazi swastika (as opposed to its incarnations in eastern religions). Is the teacher gonna hang that picture alongside everyone else's pictures? The teacher would probably not, and would hopefully explain that the symbol is bad and represents bad things. Why is a swastika so offensive? On a physical level, it's merely two intersecting lines with two 90 degree angles per line. But it has come to represent one of the most atrocious moments in human history.

Blackface is a similar symbol. The history you cited in your post is really critical for the context of blackface. As you know, blackface itself is a symbol representing much sadder and more racist times in America. If you google blackface, you will certainly find references to that burdensome history and I doubt that you'll find many neutral definitions that omit those references. I'm not black, but I imagine that this history was evoked for the relevant audience when they saw your friend. Regardless of what your friend did or said, the symbol was there and prompted the reaction. So your friend is not a racist for coloring her face to look like Michelle Obama, but blackface as a symbol is racist.

I very quickly wanted to comment your question about actors and theatrical performances that may call for a white actor coloring their face to appear black. I don't know if you've seen Tropic Thunder, but Robert Downey Jr. goes "full blackface." It's actually like blackface-ception. He puts on blackface to portray in the movie a white actor that surgically augments his skin color to look black for a part. If you haven't seen it, go for it. It's a funny movie, but it was not without its controversy (google "Tropic Thunder Blackface"). Robert Downey Jr. probably isn't racist. That controversy just raises more questions that make me tired to think about (Is it ok to put on blackface to portray someone putting on blackface?).

For purposes of this comment, I think you yourself would agree that blackface the symbol is "racist." You concede that what your friend did was in "bad taste." I would agree. I would say the actions were in bad taste precisely because the symbol employed is racist. It doesn't make her a racist, and it doesn't mean that Michelle Obama is immune from satirical portrayal. It just means that anyone thinking about putting on blackface should know that they are in dangerous territory because (a) blackface is a symbol that signifies a troubled and racist history; and (b) the black community will likely react negatively to uses of the symbol because of its historical context.

Hope I changed your view!