I read this thread and at first I thought why should we continue to the English language but then I realized that we should clarify things because it's important for discussions like this one so everyone is on the same page for advice and information.
First, Matt I'm glad your female is doing great and keep doing what you're doing. I don't see an issue currently.
Secondly, size is not a synonym for length or weight really. It's it's own word with it's own definition.
UNIVERSALLY it's used as a measurement for both length and weight combined.
We don't walk into a store and ask "what size is this shirt?" Expecting someone to say "It's 30 inches from neck line to the bottom."
We ask because we want to know if it fits our SIZE (both length of body and weight of body)
Example, in my Adonis type body shape I'm a medium and rarely a small because I'm short. When I'm sporting a dad bod I jump upto a medium to a large SIZE. This is because it fits my dad stomach and my smaller stature.
So I'm sorry BSG but in your small circle of friends you're going against the norm of the words you're using to define length and weight. Personally, and many others, would simple use the word length or weight if we were talking about one individually.
And just because I always like proof here's a link to the known synonyms of the word "length". Note, size is not listed.
Length Synonyms, Length Antonyms | Thesaurus.com