i was the same way with my first child, op, but i am not with my second. we have a life we have to be present for, and my friends and their kids, and dd and her buddies are all constantly swapping one thing or another. ds is nursing, but still has had 4 colds and a double ear infection in his first year of life.
it's harrowing, having a sick baby. my nerves still are raw taking care of my LO's, even after some years of experience. you can't keep em safe from every germ all the time. i sure wish it were so...
i feel like there is an unspoken rule about colds-where if there's clear snot/little cough it's ok. i would say something if it were my kid, and would expect the other person to let me know if it were theirs so i could opt out if i chose. i do think the mom shouldve mentioned it to you, but i dont think i'd be furious at her for not.
can you PROVE the cold came from her kid? it is cold season, and germs live on all kinds of stuff and in the air. couldve been someone else.
i got fired up recently b/c a friend brought her kids to play w/ mine right after getting a live-virus, shedding flumist shot. my kids both came down with the flu a short time after. i was livid, and i posted about it, and was reminded that i had no way of knowing that was her kids that passed it. it was flu season, and it couldve been any doorknob or grocery cart handle or whatever. then i remembered their music class teacher had been out the week prior with flu. coincidence. or not. she's a friend, and wouldnt have willfully exposed my kids to the flu, and it wouldnt have done any good to be mad or say something to her. im SO glad i didnt jump on her before i posted. i never said anything about it to her.
i hope your LO feels better soon! all the colds and illnesses, they do actually strengthen the immune system...so i hear.
oh, and hey, some unsolicited cold care advice-have you tried using nasal spray saline and then the aspirator? you get about ten bajillion times more guck out that way-our ped showed us how to do it when poor ds had his first cold at 2 weeks old. you hold babe at an incline, squirt squirt, and suck suck. it sounds a bit barbaric, and i HATE to have to do it, but wow it works, and the baby can breathe, so you can all sleep.