Isabella, ask your mother in law what kind of trees and shrubs she has in her yard compared to what is in the neighbours' yards. also, standing water will attract skeeters. most likely a combo of those two things is why she's bombarded while the neighbours escape the wrath.
i HATE mosquitoes! i'm super sensitive, although not allergic, and any bite will swell up and itch like mad, much worse than other peoples' reactions, and even those topical 'stop itch' treatments don't help worth a darn.