That is an excellent point! Ma Kent is certainly a seamstress who could tailor it -- my inner fanwank was that she'd made it a bit big on purpose so that Kara *could* grow into it. She raised Clark; she knows how big Kryptonians can get, and there's limited amounts of Kryptonian cloth. (Unless we're in the part of canon that says the AI makes the fabric now... ? I'm never sure.)

*nod nod* The suit doesn't look very... sleek might be the word? But *she* looks fantastic.