Very interesting - your DD's highest area was my DD8's lowest area!
I have no idea whether high WMI is actually associated with giftedness in math skills, but I can relate my DD8's experience with a relatively LOWER area in WMI, FWIW (WMI is "high average," but still AVERAGE):
Math has NOT been an "area of confidence" for her up until this year, but she tests very well in math (ranging between 98-high 99% on standardized tests) and has always been in the highest math group since differentiation in math started. "Quantitative" was her lowest area on the CoGAT, although it was still quite high. DD's recent EXPLORE math score was above the DYS criteria, but only her 3rd highest score. Also, DD has been making remarkable progress in math, and this year scored a VERY HIGH 99% on MAP math (with a RIT very high several grades up).
So while high WMI might indicate mathematical giftedness, lower relative WMI does not seem to indicate, at least for my DD, actual mathematical weakness.
It sounds like your DD had some subtests that were very high and that her VCI and PRI were each dragged down by a single weaker subtest. I wonder if something just did not "go right" for her on that day, for those subtests. I wonder if when eventually retested down the road, she might actually test much higher. I would also look to the other data you have on your DD to see a more complete picture of her strengths - because she clearly has many!
