A QUIET PROTEST
You may know the phrase Dulce et decorum from Horace, or from its appearance in a bitter war poem from Wilfred Owen. “It is sweet and decorous.” Dulcius is the comparative form, and with the ablative urbe it means “sweeter than the city.” The Roman worldview was so centred on their own city that urbs could also simply mean Rome, so you could translate it accordingly here. A villa is a country retreat, then as now, in which wealthy people could lead a quieter life for a time. That’s not what Sulpicia wants.
Apta means appropriate, or apt. Puella is a girl. An is one of those question words which pushes for a particular answer (in this case a no). An sit: “Could it be?”
Dulcius urbe quid est? An villa sit apta puellae…?
What is sweeter than Rome? Could a villa really be fit for a girl?
Ager, as in agriculture, is a field or farmland in general. Amnis is a river or stream. Arretium (modern Arezzo,) was about 250 miles from Rome. Frigidus, of course, is freezing.
Dulcius urbe quid est? An villa sit apta puellae
atque Arretino frigidus amnis agro?
What is sweeter than Rome? Could a villa really be fit for a girl? And the freezing river in Arretine country?