Hi, and thanks for your medical question on eHealth forum!
Take your mother to her gynecologist. The first thing to be ruled out is hormone imbalance of menopause. If this is caught on tests like FSH, LH, estrogen and progesterone level, then hormone replacement therapy will help.
If this is ruled out then hypothyroidism, hyperthyroidism, diabetes, and exacerbation of rheumatoid arthritis will have to be ruled out. Since a confirmed diagnosis cannot be given on net please discuss these possibilities with your mother's gynecologist once. Hope this helps. Take care!