My black lab seems to be in the dying process; she has stopped drinking or eating about 3 days ago. She just lays there and breathes. She initially began to lose weight and soon seemed to lose interest in eating much. She then got to where she couldn't stand or walk. She is about 9 years old so I'm wondering if she is going through the natural process of dying. I think she is now in the starvation mode. If so, how long might it take her to die? As I said she has not eaten or drank anything in about 3 days now. She has lost her muscle mass/tone.

You need to take her to the vet. There may be a cure for whatever is ailing her.

Get her to the vet.
9 is really not that old for a lab, you need to take her in and get her checked, it could be that she is suffering from an age related disease, like diabetes or kidney disease.
You should have gotten her in when she began to lose weight. Catching things early on gives her a much better chance of being treated for these diseases and giving her back her quality of life.
Please take her in.
How long has this been going on?