It could be the puberty thing - she definately has most of the beginning signs and has for a while.
Ok so I looked up a chart for average height for girls and this could explain it...
7 Yrs 43 ins
8 Yrs 45 ins
9 Yrs 47 ins
10 Yrs 51 ins
11 Yrs 52 ins
12 - 13 Yrs 60 - 63 ins
14 - 15 Yrs 63 - 64 ins
It seems each year is about 2 or 3 inches or so, except between 11 and 12 - at the low end it showing a spurt of 9 inches-- could that be right?
Any way my 11 year old appears tall on this chart - but she is maybe average or just a little above average when I see her with her team (but perhaps there are just taller girls playing basketball). She was 59 1/2 inches and she is 11 and 1/2 yrs old.
I do think though this chart is on low side, though other charts and grids I saw look similar.