My mother put on her ring but now can not get it off because it is to tight. How can she get this off?

Other options. If the ring is cutting circulation from the finger, be sure to seek medical attention, especially to consider cutting the ring off with a special tool.
Lymph therapy. You can see a lymphedema specialist - I used rian corp laser to help get the swelling down and removed the rings on few occasions.
Lotion. Try lotion or oil or anything else that would make the finger slippery. Also, when hands are warm they swell so cool hands would help in this scenario.