The ghost you describe seems to fit in the category of a "messenger ghost," as he seems to be trying to make contact with your mother for some reason. His presentation of flowers shows that it is a loving or at least benign spirit. Is it possible that he is a deceased relative, even from generations past?
What the ghost is trying to say to your mother is very difficult to determine without an investigation. Perhaps he is just trying to say, "I love you and I am watching over you." He certainly seems like a protective spirit, coming to comfort your mother in her illness.
How can your mother find out what the spirit is trying to tell her? You might consider seeking out a psychic medium, although I'm somewhat reluctant to recommend that because it is so hard to find a true psychic medium who has a legitimate track record of success. There are a lot of phonies out there. (Never pay for one in circumstances like this, except perhaps to cover modest travel expenses.)
Your mother might try communicating with the spirit herself if he appears to her again. If she can, she should ask him what he wants, what he's trying to tell her. There's no guarantee of a response, but it's worth a try. If your mother wants the spirit to stop bothering her, she should tell it so. She could say something like, "I appreciate your watching over me and the gesture of the flowers, but there's no need for you to continue to appear to me. Thank you, but I'd rather not see you again."
If there really is a message that the spirit needs to communicate, he might successfully do so in a dream or some other symbolic gesture that your mother could watch for. It might also be helpful to find out who this ghost might be. Go through old family photos with your mother to see if any relative fits the description.
In any case, it does not seem that this spirit is harmful in any way, and there's nothing to be frightened of. It will probably stop appearing of its own accord, if it hasn't already. Let us know if anything further occurs.

