I've only knowingly taken a risk like this ONCE and it backfired, and I still feel really rotten about it.
I was going to said best friend's party - obviously was expected to be there and had helped set up for several days (it was a big do) and anyway, late morning of the day itself, ds threw up in the car.
I had left other ds with friend, so went there, leaving sicky child in the car, and said look, he's ill, can you keep hold of other child please while I sort him out and I won't bring him anywhere near your place or the party.
friend said sure, and I went home and dealt with ds. He wasn't sick again and was seemingly fine. Friend said, Please come to my party, it was probably a one off, he'll be Ok. I said alright, against my better judgment. Took both kids to the party. They played with other children, he'd been thoroughly cleaned up, been fine for about 10 hours and suddenly at 10pm decided to be sick again
I got him to the bathroom in time and washed the sink and so on, then separated him from the others, he went to sleep upstairs.
I was prepared for a night of vomming ahead but there was no more. However, my other child caught it so was ill the next day, as was another child who had been at the party
I felt AWFUL as I always stick to the 48 hour rule normally and it was only under duress that I ended up taking him. I hadn't wanted to. But I kind of delegated responsibility to the person whose party it was and I never will do that again.
I didn't even want to go myself!!! (I hate parties!) So. I digress. She shouldn't have done it, and you were very unlucky. I hope you manage to salvage the mattresses.