Have you tried looking for your grandmother on the 1910 US census? It should tell you what her family thought her age was in 1910.
I probably should but she died long before anyone ever thought about the Internet much less Ancestry.com, but since her birth was never recorded, there is no guarantee it’s accurate on the census, she always knew what she was told her birthday was, like said she had no birth certificate.
Most people today can’t fathom living the way people did in 1906 Florida in the middle of the woods, farming and trying to feed your family.