I apologize that I ask for help locating stories so often. I get these snippets of scenes in my head and they drive me nuts until I either figure out which story it was or ask.
There is a fire at Longbourn and only Jane, Lizzy, Mary, and Kitty survive, or so we think. Mr. B's will is read and the girls all have 20k, I think, dowries and Mr. Collins is left with a few thousand pounds that was in the household account. It turns out that Lydia left her room using a rope ladder and ran off with Wickham who in turn kidnapped her. She's held in a shack by Pemberley and found wandering by a tenant. Mrs. R. sends an express to Darcy and everyone goes to Pemberley.