Do you/your sister have Recipt?
Don't panic. if they couldn't find the file.
Do you/your sister have received the recipt at the time of I-485 / I-140 filed they sends to person who files either u or ur attorney. just send the copy of both receipt and other required document to them.
did u/ur sister file themself or through attorney? they must have copies
I know the one person here in fourm who filed in 1999 and they lost the 485 .. when they informed that they lost , he was lucky that he had a copy of 485 form copy he sent the copy to them. and he got approval quickly.
ur case is AP... and even they don't have or lost. u have the receipt. send them if they can track your files. if you have a copy of forms pettitions that would be great. to prove.
Honestly we can advise u to get a good attorney.
don't delay.... its good because atleast u came to know about missing/lost file. in middle.
Don't panic, I always advise ppl here in fourm that keep copies of ur pettitons and receipt to u.
Good Luck
P.O.J