R is the same way! She was 40 inches at her 3 yr checkup and I think she's 42 inches now! I'm 5'5" and DH is 5'9". We also don't have many tall family members except for one of DH's uncles. I always think she's going to level out in height soon but so far she's still 95%!
Re: where did this come from???
if i remember correctly, she was right at 3', maybe an inch under.
mid parental height may be more predictive than doubling height at 2.
Your mid parental height is 5'3".
You'll have to wait and see!!