Convince her to take you to Frankie’s Fun Park, where you will play mini-golf, ride go-carts, and earn tickets while playing arcade games. Use said tickets to purchase strange, creepy-crawly things from the ticket-taking lady.
When you get back to your sister’s house from all your amusement park fun, find convenient place to stash your winnings, like her favorite over-sized coffee mug/kitchen catch-all, located in a somewhat visible place.
Place the creepy-crawly things into said mug, wander off to play the Sims/eat your dinner/sleep the sleep of innocence, and forget about them in a matter of minutes. Then, a few days later, board your airplane to take you back to the other side of the country, leaving your creepy-crawly friends right where you left them.
Upon discovery, big sister eventually locates creepy-crawlies and cringes at their realistically rendered forms. She will then more closely investigate the contents of the mug, where she will find the single thing that creeps her out more than the real thing: a plastic spider. Once she realizes she is holding a plastic spider, she will shriek at the top of her lungs and fling the horrid thing halfway across the room, where it will land in an eerily natural pose on top of her newly purchased lemons.
Bound and determined to do the sisterly thing, no matter how sick to her stomach she may be, big sister will then bag the contents of the mug, evil plastic spider included, to eventually be shipped back to little sister.
You didn’t expect her to pick it up with her fingers, did you?