Hi @dla1989. Follicular lymphoma is a type of blood cancer that starts in the white blood cells. It’s usually a very slowly developing type of disease, taking a long time to progress. Your mom may have had this for several years before her diagnosis.
Unfortunately with any lymphoma, fatigue is part of the makeup of the disease. How are her other blood numbers? Is her red blood count normal or is she experiencing signs of anemia?

Posting a couple of links for you on Follicular Lymphoma.
This from Mayo Clinic: https://www.mayoclinic.org/diseases-conditions/non-hodgkins-lymphoma/symptoms-causes/syc-20375680

This from Healthline.com
https://www.healthline.com/health/follicular-lymphoma
The type of follicular lymphoma your mom has may determine what type of treatment, if any, her doctor is recommending. Is she on treatment now or in a watchful waiting period?