"fino a" is a form of prepositional phrase (locuzione preposizionale)

• check this link http://grammatica-italiana.dossier.net/grammatica-italiana-12.htm under Locuzioni prepositive -- gruppi preposizionali for other examples.

http://en.wiktionary.org/wiki/fino_a

To say "until at dinner" is redundant. The word "until" already incorporates the literal meaning "[temporally] up to dinner." Thus, to say "until at dinner" is akin to saying, "up to at dinner [time]." Does that help? (:

That would be "la ragazza aspetta la cena"; "fino a" means until or up to, so the girl is waiting until dinner is served.