If you are just for contingency wearing for only a few minutes, it is not a big problem, but certainly you should not be for long-term wearing. Although some people say it will be ok to interchange the same two prescription glasses, you should pay much attention to it. If you wear others' glasses, your vision may be easy to decline. firstly, you should know whether you ensure the new spectacles accurate and do not underestimate this problem, because I have suffered the losses. Secondly, in addition to the prescription, the pupils distance is also a very important indicator. Therefore, do not try others glasses although the prescription is the same.
If you have the same prescription with your sister, the eyeglasses can be OK to wear for the vision. However, there is another point of appearance of the eyeglasses. As we know, we will measure the distance between the two eyes when having prescription eyeglasses. If your sister's eyeglasses are not coincided with yours, you may find the nose prints after your wearing for a long time.
I do not think it is OK to wear glasses that are not yours. Maybe you also can see clear when you wear your sister's glasses, but it is not good for your eyes. Our eyes are not important and we need the exact prescription for our eyes, not the similar ones. And if you wear this kind of glasses for a long time, you will have bad situation, like heavy prescription or other diseases.
In most case, your eyes will be hurt by wearing someone else's glasses. For example, your eyes might tire faster, and also you might get a headache. Because there is some difference between every glasses, etc, your eyes have different prescription compared with others, you had better go to hospital to know you have a weaker or stronger prescription, then the pros will advice you get a pair of glass that matches you and your eyes. Of course, now if you just wear your sister's glasses for a short time, it will not do permanent damage.
For me it wasn't. My first year in college I knew I needed glasses but was afraid to get them. Well a classmate new I was having problems seeing and brought in an old pair of his glasses and told me to try them on and see it they helped. I tried them on and couldn't believe the difference and found I could see the board in the lecture hall without any problem. I ended up wearing them for the semester before I went and got my own glasses. I found out that the glasses my friend had loaned me was almost the same prescription that I ended up getting.