Imagine you are a petite, high school girl named Brooklyn. You also happen to be a superhero, and your power is speed.
You were on a mission to investigate a suspicious politician with your best friend since kindergarten Amanda and her boyfriend Brian (a shape shifter and heat controller respectively).
It turns out that the politician is up to no good, and you are captured. Your friends are sedated, to keep them from escaping, but you are contained more easily; just shackled to the wall. You can't get out.
A timer for a bomb starts to tick down. At super speed, ten seconds seem like a long time. There is no hope of escaping without help.
6.75 seconds left, and the impossible happens. Someone runs in, so fast even you can't see her properly, and frees you and your friends. You escape in the nick of time (your friends were carried out too), and pass out as the building explodes dramatically behind you. Your last thought is that your rescuer looks oddly familiar...
You wake up in a motel room. Brian is still asleep, but Amanda is up, and she has tied the rescuer to a chair. She has good reason to be suspicious; the claim your rescuer is making is far-fetched even by your standards.
She claims to be you, from about 5 years in the future. So far as you know, time travel is the stuff of science fiction.
She looks the part. For half a normal second, you thought she was a younger version of your mom. She remembers everything you do about your childhood. You ask her to try to predict something, but she can't. She says all her memories since a couple hours ago were suppressed, to keep her from changing the future to badly. She says she came back to rescue you, and then do something else that she can't remember.
Amanda thinks that she's a telepathic power mimic that shape shifted to look like an older you.
How can she prove she's not?
- You don't want to risk untying her (but it might be necessary)
- You can't call in for help, since you've discovered from the news on room's TV that you and your friends are being blamed for blowing up the building
- You should avoid leaving the room or getting separated from your friends
- She couldn't bring anything back from the future
- You all your cool gadgets were confiscated when you were captured
This question is different from How do you prove you're from the future? because that question assumes you have lots of resources to prove yourself with, while in this situation you have very few. I don't think any of the answers fit within the limits here.