Is my friend avoiding hanging out with me I need advice

I'm friends with one of my sister's friends, and the thing is, I invited her to a haunted house. She said yes, that was about 3 or 4 days ago. So, we've decided that we'd go on the 4th. But every time I ask her about it, she says she doesn't know. We work at the same place. I called off work on Friday on my schedule because I thought we'd go that day, but she didn't call off. And she keeps saying she doesn't know if she can go yet. It's in two days from now.