Supergirl walks in and stops "The game's up Selena, you're going to jail!”.
"I don't think so Supergirl”, Selena relpies, “You see I happen to know that although you have all those powers, you're still vulnerable to the dark arts of magic, so you'll have to get out of YOUR jail before you can take me to mine!”.
She casts a spell directly at Supergirl, which magically and instantaneously mummifies her (still in costume including cape).
Supergirl instantly reacts and tries to escape. She grunts and grimaces, trying with all her might to escape her cocoon, but she is unable to break free because the wrap is laced with kryptonite and has weakened her. “Oh my god! She exclaims, it's kryptonite!”
After about 30-40 seconds of struggling Selena asks, “What's the matter Supergirl?”, “Are you a little... Stuck?”. “When I get out of this, Selena, I swear you're going down!” she replies.
“Oh dear, dear, dear, Supergirl, wrong choice of words darling.” Selena replies, “For one thing you won't be getting out of that, I'm sure you know that as well as I do. Secondly I think you'll find it's you... who's going down... quite... literally!” She casts another spell at the ground where Supergirl is standing and transforms it into quicksand, making her begin to sink to her doom.
Supergirl looks down at her feet as they disappear under the sand, and then looks up open mouthed at Selena. She is in shock and speechless! She quickly pulls herself together and tries harder than ever to escape, but it's no use. She is getting weaker and weaker, and to make matters worse she is actually starting to feel pain in her muscles as they start to tire out.
Selena lets out an evil cackle and grins with delight at watching her nemesis face certain doom. Suddenly a phone starts ringing in the background. “I'm sorry Supergirl, she says, I'm afraid I must go and answer that as I'm expecting a terribly important phone call. I'll be back later. Don't go anywhere, will you?!?”.
This was a fan custom and looks super awesome! Maybe we'll get a chance to see Supergirl again sometime.