I'd not worry too much. My DD who just turned 5yo weighs under 16 kg and has hovered around there for about 2 yrs now. She was a slow weight gainer and dropped into the 5th percentile quickly. I used to stress about it but there was nothing I could do. DD is just a small eater and is petite. Given your DD eats meat and other foods plus still BF I don't think there is anything else to do.
I relation to the walking, they do that in their own time, something clicks and off they go!

If it is truly bothering you, get a referral to a pead. GL