She sounds like a very, unpleasant little girl
Well at leasr she's only six, you're a grown woman on line saying horrible things about a child. What's your excuse?
Op, yes, it's fairly normal at this age to start noticing bodies and to comment. Unless you explain to her how it makes you feel and others feel, then she is not to know. It's not something you're born knowing.
As for the obese thing, yes you may be, you may not be, you need to do the Bmi calculation and see if you're Bmi is 30 or over.
I'm sorry, but size 16 at five foot two is probably very overweight, and this may be why she is commenting. Either she's seen it on tv, or a friend has commented.
Talk to her gently and try not to let your own sensitivities get in the way.