I need help! My SIL bought a pair of $120 jeans
and needs to hem them up about 3 inches. She wants to wear them Friday night for her Birthday Party. She came to me to help her and I'm so afraid to touch them. She thinks if we pin the existing hem to where the right length should be and sew it then cut the excess fabric off inside the jeans it should work. That does not sound right with me so we're asking for some opinions. TIA
and needs to hem them up about 3 inches. She wants to wear them Friday night for her Birthday Party. She came to me to help her and I'm so afraid to touch them. She thinks if we pin the existing hem to where the right length should be and sew it then cut the excess fabric off inside the jeans it should work. That does not sound right with me so we're asking for some opinions. TIA

I am not a seamstress at all and just don't get it! 
Can't speak for BibbidiBobbidiBOO. 
I would be rolling around on the floor too!