Your mother should have an immediate evaluation as a followup of the bypass. The symptoms are not inconsistent with heart failure. Often elderly individuals do not have any chest pains the classic example of heart failure.
People with heart failure may find that they often feel cold in their arms, hands, feet, and legs. This happens because the body is circulating most of the available blood to the brain and other vital organs to compensate for the failing heart's inability to pump enough blood to the entire body. As a result, the extremities get less blood, and without blood to warm them, these parts of your body feel cold.
Heart failure can backup blood and fluid into different parts of the gastrointestinal system or abdominal cavity and the result is a loss of appetite
Fatique can be the result of not enough blood/oxygen to the skeletal muscles. I can't think of any other cause for those 3 symptoms. Does your mother have a fast heart rate (over100 at rest)? Is there any swelling of the ankles?.... The low numbers of blood pressure may be ruled out and usually not significant unless she feels the effects of this, which are usually not fatigue, etc, but more likely to be dizziness, etc.
I agree with the other responses. You may want to contact the doctor or nurse with a telephone call. There may be something else going on, but the symptoms are serious and warrants medical consultation. Thanks for sharing, and keep us informed
I think maybe a Doctor needs to assess her and check her medication. It could be anything from low blood pressure to a problem with the grafted vessel.
Is she willing to be checked by her doctor? A sudden change like this isn't good. Don't talk about moving her to another place. That's the last thing an older person wants. My Mom is 82 and refuses to even discuss it. Just let her know you're worried and want her to be comfortable, not freezing all the time and feeling crummy. She may be more responsive to your concern that she get her pep and appetite back.