Some help? My wife got bit by some kind of bug..The spots on her legs are necrotic...doctors baffled. Details inside.

She fell asleep on the floor of our cottage in Ontario, Canada. When she woke up it looked like she had 3 burns on her legs - water blisters etc. Then they turned black, first doctor said they were not burns, and gave her antibiotics. 2nd doctor said the same and gave her MRSa - level antibiotics after seeing the results of a swab (Several types of venom and some e-coli) - and yes we know about recluse spiders. Docs have no idea what did it, but think skin grafts may be required after possibly months on antibiotics. Anyone with any insight on this? Thanks in advance.

(I can get you details on the test results, but not right away as I'm at work).

tl;dr: doctors clueless, my wife's legs have black holes in them from mystery bug.

Edit: thanks for the help so far; also, she has fairly bad excema which seems to make her skin very vulnerable to what otherwise might be mild things...but necrosis is a bit much...