HALLUCINATIONS!1 high temperature can cause that
Possible visitors, of some who passes, maybe even relatives. Were they ghosts, well define ghosts... I think they definitely were spiritual in nature. Messages, well yes sort of, but only your Mom would know. Hallucinations? Well they were most likely induced by her temperature and any meds, and then maybe not. What she heard may have been a delusional interpretation of a sound.
I feel we often have others for the spiritual side looking in on us. There is a lot that we humans still do knot know nor are capable of understanding yet.
Hallucination... But ultimately, dreams are about the dreamer.
Whichever is the most likely answer is probably the correct answer. It is far more likely to be hallucinations than anything else.