Dear Kay, I'm so sorry to hear of your father's passing. I know you and your family are still in great pain. Please know that I'm praying for all of you and your beloved father too.
Right now your mom might need a little time to heal before putting her energy into a workout program, but when she is ready, she would benefit greatly from working out as it will be a good stress relief emotionally and physically.
She needs to start easy with walking or water aerobics no more that 3 times a week for the first three weeks. After that she can gradually add on a day or two as/if she feels ready, but not necessary to add if she doesn't want to.
In addition to her cardio classes she should participate in a beginners program for basic weight lifting. Do you by chance have a Silver Sneakers or Healthy Bones program for seniors in your area (usually held at YMCA's or fitness centers). That would be perfect to do one to two days a week too. Another valuable source would be to get a certified trainer who specializes in senior fitness programs to get her started. Then she can continue alone so that it doesn't become too costly.
I hope this helps. My prayers are with you all.