I had no idea that the sibling rivalry would start so soon! Jack's only a year and a half and Olivia has been waiting the entire year and a half for her brother to be old enough and interested in playing with her. Now that he's to that point there are times when she doesn't want it.
Olivia has started the I-don't-want-Jack-in-my-room phase which will probably last for the next 15 years. I know that my children each need their own personal space, but I also feel like it's important to share and part of that means letting your brother come in your room. So the rule I started with Olivia is, "if you have gone into Jack's room today, then he's allowed to go into your room". It seems to be working for now.
When Jack is in Olivia's room and annoying her, she reacts by taking whatever she is playing with to the kitchen table or somewhere else that Jack can't reach. The other night she was playing Littlest Pets and Jack was in her room "wrecking" it so she brought it downstairs to the kitchen table to play by herself.
It didn't take too long for Jack to realize this so he came into the kitchen and climbed up on the table to play with his sister.
Jack the spectator
Here is where he starts to disturb her and she stops him
He decides that he'll just annoy her by peaking through the window
...and while she's not looking, he'll reach through the window and steal whatever is within reach
The I'm-up-to-something look
Olivia takes action, trying to push her brother back
She finally realizes that he's not going anywhere and he might be a good playmate so she let's him play.