When should I get concerned about a friend who is not responding to me?

Last week one of my friends asked me if she could start going to the gym with me. I agreed, and she wanted to go some time around 5 today. Cool. The plan was to meet at my place and head to the gym from there.

Around 3 I text her to confirm that she still wants to go. No response. 5pm rolls around, she doesn’t show up and still no texting. I know that she is quite busy with school/work but it is very unusual for her to not at least reach out. I text her again just to check in around 8…that was about 3 hours ago, still no response.

I’m kinda starting to get worried? Am I being paranoid? It’s unusual for her to miss something, and extra unusual for her to not at least text me. It’s fine if she forgot/decided that she didn’t want to go, but at least reach out. Maybe I’m just being weird about this?? If so, when should I actually start to get concerned?

Marking as NSFW due to implied potential harm.