To say Lyra is jealous of Twilight going to the human world is an understatement. She is so jealous that she decides to find her own way there. Using an ancient spell book, which she “borrowed”, she soon creates a portal to the human world.
Too bad it's not the same one Twilight was in with colorful people who look exactly like her friends. In fact, it looks more like ours.
Now after having her fun here. She decides that its time to go back home. But a group of snooty popular girls, an oppressive dean, and a corrupt student disciplinary committee prevent her from even getting near the return portal. In order to do this, she obtains the help of 3 genius slackers. With their help, she faces the dreaded challenge of surviving high school all over again, learning all kinds of human advantages, and hopefully finding her way back to Equestria.
If they don't find out who she is first.
It suddenly occurs to me that it won't work. Why? Because the portal changes humans to ponies and vice-versa. So, anyone Lyra brings back with her from either Earth or EqG pseudo-Earth will turn into their pony equivalent going through the portal!
Sucks to be her!
Okay no. Just no.
There are multiple problems with this.
1. Your grammar, spelling, and for that matter your actual writing suck flaming monkey ass. You need at least two editors to help you.
2. Excessive fanon abuse. Your Lyra is basically a flanderized version of Anthropology Lyra. Only really badly done. Same with Bon Bon.
3. Inexplicable jealousy and hatred of Twilight Sparkle. It just comes out of NOWHERE and it feels wrong.
4. MASSIVE plothole: Lyra doesn't need to prove humans exist. Twilight Sparkle already proved it. Anypony can just ask her about it.
5. Critical logic failure. Any portal into the world Twilight went to would turn a pony who went through it into a human, and any human who went through it into a pony.
Wait. If a pony like Fluttershy or Rainbow Dash went through the mirror, their human selves would disappear. Is that your theory? I highly doubt that.