Could you suggest that when she is not well you all go to see her? If you made it just a day trip that would cut down on the length of time she was contributing her cold germs. Get DS a "special spoon" of his own to use, so that she is not feeding him tasty morsels with the cutlery that has just been in her own mouth.
You need to be tactful and devious, I think.
To go through chemo therapy or choose not to?
Have any of you got all electric cars? Pros and cons please.