Considering her age and the symptoms, my concern would be possible congestive heart failure or some cardiac issue. Of course, it could be many things. Some conditions of old age, like in people, can be managed with medication if caught early enough. I am nit sure when she last saw a Vet but it might be a good idea to take her in for a check up.
A visit to the vet is most definitely in order. An accumulation of fluid in the abdominal cavity can be caused by a few different things, most of which can be quite serious and need attention immediately.
She will need bloodwork to make sure her liver is functioning correctly. Ascites, or abdominal effusion, can be caused by abdominal cancer, low levels of protein in the blood (hypoproteinemia) or right sided congestive heart failure. It can also be caused by a ruptured bladder, which seems unlikely in her case because she is acting normally and doesn't seem to be in pain, which she would be with a ruptured bladder.
The vet will have to remove some of the fluid to analyze it to see what it is comprised of, and from there they will be able to tell which route of treatment will be necessary.
Please keep us posted as to what you find out when you go to the vet. I will keep good thoughts for Maggie and for you.
My advice is to take Maggie as soon as possible to the vet and ask for an abdominal ultrasound, particularly of the spleen and liver. Golden Retrievers -even happy wagging healthy ones! -are very prone to developing bleeding tumours on the spleen. Some of these can be 'slow bleeds' or slight bleeds, and if it was caught early it might give her a better chance.
I am not diagnosing, or saying it IS DEFINITELY that, but it would be wise to investigate.
Bless her, and I hope she continues to be well for a long time to come.
I'm sorry it's taken me so long to update.
Maggie's visit with the vet went well, although, we received some pretty devastating news.
Maggie has been diagnosed with congestive heart failure.
Her heart is enlarged, however blood tests determined no other organs are involved.
Her vet was shocked to remove 14.8 lbs of fluid buildup from a dog who was showing no major symptoms other than a very slightly distended abdomen.
Her vet prescribed a diuretic as well as Benazepril in the hopes that we can avoid additional fluid retention and extend her life by a bit.
However, her prognosis is not good. If the medication works perhaps a few months, if not, perhaps a few weeks.
Maggie is at home resting, staying as calm as possible, enjoying lots of boiled chicken and rice, many cookies and being the wonderful girl we love.
Thank you for your knowledgable advice.
I am so very sorry that the news you received was so bad. As much joy as our pets bring us it never ceases to amaze me how quickly things seem to go south when they decide to.
I pray that Maggie's medication works and that you can still have lots of quality time with her, loving her and spoiling her. Be diligent with her dosages and just spoil her rotten. You'll never regret it.