Amanda. Those are fun things your Dd is doing! What I want to say, from my perspective of a math person, is that I don't see the socks/eating examples on the first post as subtraction. What I see is that she has the one-on-one correspondence very well mastered. She probably could mentally match the socks with her limbs and see that she had an extra one. I don't think it shows that she did 5-4. In any case, that very strong concept of correspondence does show to me strong math abilities.
Both my dds were not early counters, but my oldest always showed very clear understanding of concepts. She could add/subtract numbers to 10 (when she could count to 10), and higher when she got the rote counting down. FWIW, the oldest dd was just tested (IQ/achievement) and she did really well in math (99.8 percentile, just one point shy of YSP requirements, which she got in the other areas).
Anyway, what I learned from her is that those strong comprehension of math concepts and ability to manipulate the numbers were what was different. Kids that could count higher than she did when she was younger turned out not to be smarter or further ahead in math than she is. Oh, and just to clarify, it could have been that the early counters we know IRL would have been HG but they were not, some are MG and some are not.
She also was rote counting to 100 before 2yrs.