M.P.
She's perfectly fine. I had a 21 lb 9 month old and a now 20 lb 22 month old. Both are still breastfed and my little one who nursed more hardly eats food at all so it's not just breastmilk, it's genetics.
It's a fallacy that all babies at 6 months old need solid food. They don't. Gerber made us believe that :)
Maybe a formula fed baby is different but milk is a more than sufficient diet for an 8.5 month old.