J.P.
She may not want visitors while getting treatments. My grandmother had cancer and it was awful to see her so sick, she didn’t want too many people around her. She may also feel embarrassed with how the treatments affect her. I would just continue to let her know that you are there if she needs anything. I can also understand why she would want her son back in school and not see her this way.
There is something else to consider. If she is getting chemo then she is better to stay away from anyone that could be sick. It drops the immune system even if she is receiving small dosages.