Is my sister saying that purposly?!

Like the other answerers said, she's young and she'll say what she wants regardless to whether its the truth or not. My little sister went through a phase like this when she was about 5 or 6. But not only girls, she would say everything was sexy.
"Grandpa's glasses are sexy!"
"That lamp is sexy!"
"You're sexy!"
"She's sexy, he's sexy!"
You get the point... I think it's just a phase, because she's eight now (she stopped that a while ago) but right now she is obsessed with the computer.
But yeah... It seems pretty normal to me.

Just roll with it, little kids rock, they say what they want, regardless of it being true or not.

When I was a kid I would imagine I was a character from a show and go save the day.... yeah lame but I LOVED IT, and even better, i turned out just fine... well, as fine as fine can be!

Good luck, and btw, I would ratehr that then the little sibling who don't shut up about like... trains and **** :/

okay, 1, i think its odd that she knows what those words mean. and two, nah. nothin's wrong with her. she's just bein a kid. I mean, kids go through phases. but if this problem persists, you might wanna see what's up.