Sometimes you get sick just like anyone else, but unlike children or other healthy adults who can recover quickly if they happen to catch your illness, elderly people recover slowly, and possibly with serious complications. This is especially true if the elder has a chronic respiratory weakness (as Mom does here).
So what to do about it? Other than the obvious thing of having separate kitchen times, consider wearing disposable gloves in general and a simple dust mask when you are in the unavoidable situations where you have to be in talking distance of each other. I also wipe down all surfaces that I touched with disinfecting wipes and spray disinfecting aerosol in the breathing space we both pass through. Both the wipes and the sprays are available at low cost in a variety of pleasant scents. The masks are available at hardware stores in multi-packs, and gloves can be purchased at medical supply stores.
Yes, it is an extra hassle when you are already hassled by being ill, but better to be cautious than trying to deal with a situation.