@Bronte1985
I'm curious to know which art history PhD programs you consider to be "top". I'm a recent graduate of Columbia's MA program (I can provide details to the OP in a follow-up post) and have known several alumni to go on to PhD programs at Harvard, Princeton, Stanford, Northwestern, Columbia, and UPenn, just to name a few.
I think you should absolutely keep the course and that you're not risking anything by doing so. Earning a B in a class is respectable and should not cause an admissions committee alarm; they understand that grades fluctuate. I have grades across the board on my undergraduate transcript (due to some factors out of my control) and that did not keep me from being admitted to Ivy and Ivy-caliber schools for my graduate studies. Committees will want to see you took a range of coursework and that those classes inform your research interests (which it appears the course in question does). Don't be stressed over one or two grades that may not match your ideal.
Does anyone have a sense of the timeline for Yale interview requests? I'd be a bit surprised if one comes my way, but I'm still on pins and needles, nonetheless!