だって、四次元ポケット持ってるじゃん。ドラミちゃん歌もうまいし。楽しいって。
Datte, Yojigen Poketto motte ru jan. Dorami-chan uta mo umai shi, Tanoshii tte.
Because she has the four-dimensional pocket. Dorami-chan is also good at singing. She's fun, I'm telling you!
Uta - song
umai - skillful
How can a song be skillful? I'd understand "utau koto ga jouzu da shi" because "utau" is a verb, "uta" is not.