If it's already been rejected for "reused content", even if your sister has given you the channel it won't do much good to connect it to your own AdSense unless you correct the reused content situation.
Yes; you can connect it, but this is likely to reset the entire review process back to day 1 and send you to the very back end of the review queue.
The good thing is that this will give you plenty of time to delete the violative content and create new, original videos that YouTube will see as monetizable. Please don't think that you can just take over this YPP-rejected channel and get accepted for changing the AdSsense association and reapplying with the channel "as-is".
You're going to have to do some work to make the channel into something acceptable to the YPP review teams.