Could the words “la mia ragazza” also be used to refer to a daughter? Or does it exclusively refer to a girlfriend?
For example, in this context, a person with a son and a daughter.
“In questi giorni sono coi miei figli... Tra il lavoro e i loro impegni ho sempre pochissime sere libere. Mi fa sempre piacere passare il venerdì insieme, ma la mia ragazza è un po' gelosa e vorrei dedicarle più tempo.”
If you add the article, "la", to the phrase, then I think it has to be a girlfriend.
With family members, the article is omitted (singular cases only), and daughter is "figlia".
Ragazza is more generic, like "a little girl" when you refer to a baby or a toddler.
la ragazza = the girl, or the baby girl
La mia ragazza = my girl (friend)
mia figlia = my daughter (never "la mia figlia")
le mie figlie = my daughters (never just "mie figlie")
le ragazze = the girls
le mie ragazze= my girl (friends)
I also believe that the translation, loosely, of your example reads:
These days I am with my sons. Between work and business (busy schedule) I always have too little free time. I always like to spend Fridays together, but my girfriend is a bit jealous and I would like to dedicate more time to her.