My sister says she can't take off her contacts. Could it really stick to the eye that u can't take it off?

It can. People who either have dry eyes or are wearing tight contact lenses can sometimes have difficulty removing them. Often, placing several contact lens wetting drops will allow the lens to be more easily removed. If the contacts constantly stick, see an eye doctor about getting re-fitted.
Not really. If the eye is very dry, it may be difficult to "pinch" it for removal because it will not slide easily and comfortably. Just use rewetting drops but keep the fingertips dry so they will "stick" to the contact readily.