slwong3

Since your printer is not a network printer, it is not able to do the printing as a standalone print server.
In order for you to print, your sister's computer must be turned on.  I suggest you to create a new user account and assign your printer to that new user account.  Then you can just print documents with your computer as that new user instead of using your sister's user account.

Or else, you will have to buy a network printer which can act as standalone print server.
(In that case, the network printer will have its IP address and you just need to attach it to your router.  Then everyone on your network can print with the printer.)