Oh No! UFO! — Linda Joy Singleton

Cassie Strange is the only normal person in her family. Her dad is a TV celebrity who debunks the paranormal in his weekly cable show I Don't Believe It Her mom is a naturalist who once wore a gown of grass to get her point across. Cassie's genius brother is an aspiring actor who's always in costume. And Amber, Cassie's kid sister, has a secret way of talking to animals.
When her family goes on a camping trip, Cassie finally feels they are doing something "normal" - that is, until she finds out that the vacation is really an excuse for her dad to investigate UFO sightings in the area.
After their first night in the tent, Amber is not acting at all like herself. Cassie realizes that something is up, and she soon discovers that her "sister" is an alien imposter named Vee. Of course, her father doesn't believe her. How can Cassie alone rescue Amber before the aliens use her sister for show-and-tell?