She's playing a nerdy character. She's not going to wear outfits even as a teenager on the show that will reveal anything. At some point in the next few seasons they will do the inevitable "ugly duckling" episode where she wears more modern clothing for kids her age to get attention from boys etc. Both of those girls on the show have been through a lot in their private life.
The show overall is still good enough for network tv. There's only so many gay jokes, old man with hot wife, clumsy husband etc etc in the pipeline. Eventually you run out of ways to make it clever.