Two of your friends are fit for the word, 멋진 , according to your describing.:) As for first 언니, i think the followings like 세련된, 옷(을) 잘 입는 ,예쁜 is fits for, too. So how about putting them together in the sentence when you descirbe her? for example, 그 언니는 진짜 세련된 언니예요. 예쁘고 옷도 잘 입어요. or, 그 언니는 진짜 멋진 언니예요. 예쁘고, 옷도 잘 입고, 성격도 좋아요. Also, you can say "스타일리시해요", using the word, stylish, in especially speaking. this word, 스타일리시하다, which is not a standard word, but we say a lot like this, using the english word as it is.(loan language) for example, 그 언니는 스타일리시해요.(=옷을 잘 입어요.) I hope it helps :)

sorry! i will write again below.

First one is 맵시(있는) 언니 Second one is 당찬 언니