Mother is sleeping all day, only awake only for a few hours when she eats and bathes. Is this normal? She has lymphedema in her right leg.

AlvaDeer is correct -- you need to know what you're dealing with and this means a doctor's visit. Can't safely diagnose someone on an anonymous, crowd-source forum. I wish you success in getting answers to your concerns.

This is a question you will need to take to your Mom's doctor with your next visit. At 80 you are much more tired that you were when younger. I am 78 and now almost daily take a nap, something I never did in past life. Starts with putting the feet up to read, and boom, I am out. People often sleep more with certain conditions or chronic illnesses and people often sleep more when there is any depression or withdrawal present.
All of that said there may be a lot of hidden and undiagnosed things. Thyroid, B12 deficiency on only a few to mention at the tip of a very large iceberg. Do see the doctor with your Mom, or even have a phone conference. Try to get together any other new symptoms that have come along about the same time as this need for a lot of sleep. Is there a weight gain? Is there any sign of anemia? Any muscle aching or generalized pain. Once you have it together to talk to doctor the two of you should make a call. Good luck. Hope you will update us about what is found.
Nocturia is normal in the elderly but that is not to say, if this is a change, that a good urinalysis should not be done along with a bloodwork panel.