Every one is individual and you may not have the same problems that your sister had. I have taken Lexapro for an extended amount of time and had no side effects at all. I do take it at night right before I go to bed. It has been a great tool for me. My pdoc that prescribed it said that she chooses it because it has the highest effectiveness rate with the least side effects. She also said that if a person has side effecs while taking it they tend to go away in a couple of weeks.
Hope this helps,