Family advice please?

My fiance had his little sister over visiting at our place for some of the summer. Every year I have to get my house sprayed for snakes and bugs because of where I live (there is like a wooded area right behind where I live). She had been telling me since she got here we should get the house sprayed because she had been seeing spiders. I didn't think nothing of it and just sprayed some can bug spray around the house because we are moving soon and didn't want to waste the money. Well about a week ago she walked out on the porch without any shoes on and got bit by something. When she come to tell us she said that she thought it was one of the cats that usually hang around the house so i told her to wash it and she'll be okay. Well turned out it was a baby snake bite. She spent 3days in ICU and just got out today, I went to her moms house and gave her a card and teddy bear but now I don't know what to do I feel like complete crap! And his mom now HATES me (well says I'm a stupid female). We're getting married on the forth and idk what to do. ADVICE