You need to install the programs for only the one user, but not all programs have that option. Otherwise you have to manually move the icons form the "All Users" Desktop folder to the specific account Desktop folder. The user accounts are separate, but there are areas where you can create things that all accounts see, which is where those icons are being put.
Under the C:\Users\ there is a list of users. the game icrons are under public\desktop, and they need to be moved to "Sister's acct name"\Desktop for them to show up on her desktop and not yours.
Of course it would be easier to try and remove her as an admin... but something tells me that would cause more family strife than necessary.