Well, it seems I did use the wrong term. A blogger buddy who has lived in Mérida for quite some time and who actually speaks Spanish, tells me that La Muchacha means "the girl" and is the term Yucatecans use to refer to their household help. As we would say "housekeeper", they would say "the girl". While Daughter does help around the house, she doesn't help enough to have earned the title of La Muchacha...lol. So now I have to come up with a new name for her.
There's the ubiquitous DD...Dear or Darling Daughter, to which I would add a 3 to denote which DD. I have 3 girls, so she would be DD3.
Or YD...Youngest Daughter.
Or Hija, which my friend tells me is daughter in Spanish.
Now here's a little funny about how to say that. In Spanish, the "h" is always silent. "I" is pronounced as "ee" and the "j" is pronounced like an English "h" but it's said in the back of the throat. So it sort of comes out sounding like ee-hah. Which is remarkably close to Yee-haw. Daughter is a born comedian and we joke a lot in our family, so I'm going to get lots of mileage out of Yee-haw...lol.
So which one to use? I'm going to go for YD. It'll be quicker and easier to explain later on, should I have to.