It depends on what type of person you are and how you wear your clothes. For some girls, a pair of big plastic fashion glasses is a good fashion accessories to decorate them. And they can get more cute look from them especially people with a face features that similar to Korean. Still, some girls can get very individual look from big plastic fashion glasses. But there are some people look very stupid with big plastic glasses frames. So, you shall try on to see if the glasses fit for you.
The big plastic fashion glasses are quite popular now and you can easily find many celebrities are wearing such style glasses. But it doesn't mean they are suitable for everyone. If you have a wide and puffy face, you should stay away from them.
In my opinion, big plastic fashion glasses do look really classy. Big plastic glasses, especially those glasses in some dark colors, such as gray and black, will make you look trendy and elegant. What's more, choosing a pair of fashionable big glasses can also help to show your personal good taste.
It depends. Different people with big plastic framed eyewear gives people with different impression. As I know, big plastic framed eyewear is the most popular among students. They always dress themselves with nerdy style.
It depends on who wear the eyeglasses. I don't think they are cool with big plastic frame, but I saw some young girls with big plastic eyeglasses frame are really nice. Nevertheless, there are some people may look nerd with such eyeglasses. Maybe your sister can be complimented by her big plastic eyeglasses.