"My daughter is well behaved."
Translation:Tha an nighean agam modhail.
I'm guessing it is because of "MY daughter", so you'll have to consider the "agam" as well here. In Gaelic, when you'd like to indicate that something "belongs" to you, you follow this pattern: "an ... agam". As we've seen in previous lessons, the same goes with "my husband" for example: Tha an duine agam ann an Afraga a Deas.