Pat Brown has loads more experience and may know a lot more about this case than I do, but I don't see this as a random stranger crime.
Rather, I think MB was targeted by someone that she would have recognized had she seen this person's face. It's also possible that the perp wanted cover not just so MB wouldn't recognize his/her face, but also so that anyone attending the class who arrived early wouldn't recognize his/her face. And also, so that anyone viewing the church's surveillance video wouldn't recognize his/her face. It makes me wonder if the perp is somehow familiar with and associated with the church.
Thus the reason for the oversized and uncomfortable looking getup that provided nearly complete cover, but that somewhat impeded the wearer's ability to see or move. For example, when opening the dutch door, the perp opened the bottom only and seemed not to immediately recognize that the top had not opened as he/she almost moved forward into it before tipping his/her head to see better and realized he/she had to open the top too. The perp seemed to move through the place as though he/she had been there before, even as it looked like he/she was trying to look like a burglar.
Might there have been someone who thought it irreverent to have an exercise class in a church facility? Too loud, and too much exposed skin and immodest movements?
ETA: After posting, I checked the calendar and noted that the day this occurred (Apr 18, 2016) was a Monday. I wonder whether the perp either knew or expected that Sunday's collections would be in a safe on premises that early on Monday morning (i.e., before the counting of the collection for deposit to a bank)?