I know that some here hold that opinion, but it is not universally held. I have one kid with two WISC-IV scores: one PG and one MG. While I do think that the lower one is probably an underestimate (she had scores all over the place that averaged out to MG and she is 2e), if I'm being honest, I'd have to say that I'm not sure that the first one isn't a bit too high. I say this as a preface that I'm coming from the spot of someone who may have seen this in her own family.
An example of an overestimate (and it is probably more common in younger kids):
The vocab test asks a young kid to define a word like "therapist." This kid's parent happens to be a physical therapist. One correct answer on a "hard" word like that boosts your score by a lot more than getting one hard word right would for an older kid.
Another example:
Child A lives in an enriched environment (parents read to him a lot, attends preschool, goes to museums, etc.). His knowledge base and vocabulary and all of the parts of the IQ test that don't rely on pattern recognition (generally more of the verbal subtests fall into this area) are going to be higher than Child B who watches a lot of TV and doesn't get read to. Whether Child A is actually more intelligent than Child B, maybe, maybe not.
This second example explains why adoption studies of IQ generally show that adopted children tend to test more closely to their adoptive families on IQ measures in childhood and then regress (or go up) to numbers more similar to their birth families in adulthood. A good adoptive environment can inflate (or a poor one deflate) scores artificially especially in early childhood.
That all said, I was responding very quickly before as I was running out the door. If I had to just guess, given how high your dd's scores were on the WPPSI, I'd say that she is some level of gifted. Whether it is as gifted as those scores indicate, maybe, maybe not again. She might be more able for all we know!
However, given her school performance, my guess would be one of the following:
She is more MG than HG+ and has a learning disability
She is HG+ (like her prior scores indicate) and has a rather severe learning disability.
For comparison, my 2e kid I mentioned above, probably has an IQ right around where your dd tested (if I'm averaging the two scores and pushing it a little closer to the higher one due to variation in the scores on the second testing which still had some 19s). She is very young for grade having been started a little early (we snuck around a cut off that she missed by just under two weeks). She has inattentive type ADD and maybe dyslexia. She is, none the less, a mostly A student and is subject accelerating in math.
Where I see the major impact is wildly divergent test scores and group achievement test scores that wind up making her look like a major flake or lowering her overall grade to a B rather than an A at times. That's wherein I'd say that your dd likely has a much larger problem with a LD than does mine (more severe) should their IQ scores be fairly similar, which they well may.
