I appreciate the input.

Her wrong does make my wrong less wrong (triple negative?). In the absence of her speeding, I would have completed my pass long before we converged.

I like this trail, and ride it pretty often. I am still not at all certain that I should change my riding patterns here.

My options are (correct me if you see any I'm missing):
-don't ride the MUP
-don't pass on the MUP
-blast by wobbly children when passing to get by as fast as possible
-continue to ride as I do

And I'll point out that I was riding carefully enough that I did avoid the rider blasting down the trail, without anyone even having to use their brakes. I even did what she wanted (cooperation!).