YANBU, it's horrible when someone who has a contagious illness seems to want to spread the misery. Sometimes it is selfishness or spite, sometimes it is just plain stupidity. I do my best to steer clear of these people but if they are in your home you are a little bit stuffed.
Dose up on vitamins C and D, change and wash your clothes asap, use antibacterial wipes on every surface possible, have a hot shower and gargle some water (and spit it out) (in the sink) as often as you can. If she has infected you now there is still time to fight the cold off before it can take a hold.
With your children, it depends how old they are as to whether vitamins are suitable. For an adult you (I, anyway) can ignore the recommended doses when at risk of getting a cold. Take vitamins C & D every hour while you remember.
You can overdose on them but it is very unlikely. If you had a dozen vit D tablets every day for several months it may harm you, short term it is fine. With vitamin C, stick to the traditional tablets not the fizzy ones if you want to take more than one per day because the fizzy ones have a much higher dose. (I got caught out by taking too much vitamin C once, let's just say it acts as a powerful laxative in high doses...). Things like Vick's First Defence spray work sometimes. Again you'd have to check the packet for the suitability of it for your children.
If it sounds like I'm paranoid about getting a cold, I am! It is possible to cut down on the number you get by doing the obvious things like staying away from the infected, washing your hands frequently, not rubbing your eyes or nose. It's worth noting that colds take hold at the back of the throat and nose. Cleaning / clearing these areas (gargling water, nasal sprays to stimulate nose-blowing) as often as possible does help. Sometimes they will slip through though.
But you are right that it is at best idiotic, at worst vindictive and mean to not take simple precautions to avoid passing on a cold.
Good luck in staying healthy.