From what I have read on this forum and in other forums on the Inet, the answer is a definate maybe.
If you IOS device is one of the ones that is supported, then maybe. If not, then no.
If you have "creatively abused the game mechanics", then no. If not, then maybe.
If your sister has "creatively abused the game mechanics", then no. If not then maybe.
What do I mean by "creatively abusing the game mechanics"?
Well, as an example: the game seems to dislike time travel. People have noticed that if they advance their iPad's/IPhone's date/time. The game will pick up on that and advance the time in game by the same amount. So as an example: if you have someone in a training room and the game says it will take 4 hours before they gain an increase in their SPECIAL attribute they are training, if you advance the date/time of your device by 4 hours, then they will gain that increase almost immediately. BUT, it has been reported that this can bug the game itself once the system date/time is set back to where it should be. How severe the bug this introduces seems to vary. I am guessing on how often it is done and/or how far into the future you have gone. Basically, if you play games with the game, you run the risk of disabling something in game or the whole game.
Now, why do I say "maybe" and not yes? Well, apparently there are actual bugs in the game (i.e., unrelated to people abusing the game). At present, nobody is sure when these bugs will be corrected or what will happen to vaults when they are corrected (depending on the bug, a bug fix may force a reset). There is a possibility that you can lose gear you get from lunchboxes due to a bug or due to a fix for that bug.