How do we know when aspiration is needed?

If there is "something going around" in the SNF, she very likely has that. At her age and with her impairments it may be more severe for her than it would be for you, for example.

Is someone helping her to eat during this illness?

Yes! Mom has been in a SNF for a year and a half now. She has been on thickeners & purees. Has had barium swallow exams. She has lost too much weight now. Spits up the cough syrup. Has yellow mucous. They took a chest Xray. It seems to be just something going around, but I am wondering...

What is she coughing up? Food? Phlegm? Yellow mucus? Call the MD asap

Is she on a dysphagia diet? Have you talked to the doctor who is following her for the dysphagia? Has she had a recent swallow test? What is the basic cause of the dysphagia? Does she have dementia?

I'm not quite sure I understand your question. Are you wondering how to know when she needs a special diet to minimize aspiration risks?

(Aspiration is getting food or liquid into the lungs, which can lead to pneumonia.)