The speaker describes their younger sister in a string of short, plain statements, and the picture that comes out is far from perfect. She is chubby and neat, wonderful and miserable, kind and selfish. She doesn't like cow meat. Even her good moments are a bit uncertain, since she is "sometimes-ish" beautiful. The speaker doesn't smooth any of this over, which makes the description feel honest and affectionate rather than flattering.
The turn comes with "The point is she is my sister." All the contradictions stop mattering next to that fact. The speaker says they would never sell her out for silver or gold, and that she means "the whole" to them. The last two lines are sweet and a little playful: she loves me, and I love her more. The mood is warm, loyal, and gently funny, like someone teasing a sibling while making it clear how much she is loved.