I would also believe, as BHP39 stated, that what is called her HDL Cholesterol numbers are very low. This type of cholesterol keeps the LDL ("bad") cholesterol from forming deposits. I would agree with BHP and surfgirl that some internet research would help, but I'd stay away from any site trying to sell you something. The American Heart Association has good information. I am guessing that the docs are going to suggest some exercise for your Mom, and she would be very wise to heed it, as exercise is one way to control diabetes and also to raise the HDL level. Your mom is probably going to be pretty depressed, that's normal, she's been through the mill as we used to say, but a strong support system to make lifestyle changes is going to be really important and can make all the difference. Best wishes.
I'm so sorry to hear about your mom. Sounds like shes strong though! I think when they said low cholesterol they meant low in the good type. Apparently that is not a good thing. I think internet research is good to get a working knowledge of terms and then have a sit down with your moms cardiologist.