Ask her to invite one of her girlfriends over

You ask your sister to call Jennifer and ask her to come over. Your sister starts to pick up the phone right away and has a short conversation.

She then gets back to you and tells you she will be here in 30 minutes.

You slowly drink you coke and start to watch some television.

"I wish my sister would get on all fours and act as my feet bench."

Your sister immediately gets down and you lay your feet on her back.

After you watch television for 20 more minutes you make another wish.

"I wish my sister would leave the house again and she wouldn't come back unless I wish her to come back"

You sister immediately gets up and leaves the house again without even saying bye. You know Jennifer will show up in 10 minutes so you knew you had to hurry.