Panting and an inability to settle may indicate difficulty exchanging oxygen, but can also indicate that she is stressed, nauseous or painful.
Can you check her gum color? If they are a nice bubblegum pink then difficulty exchanging oxygen isn't likely to be the problem.
And because she can sleep fine during the day that seems less likely. I would expect her to be the same no matter when she tried to sleep.
I do believe that a geriatric blood profile may be helpful in figuring out why she is behaving the way she is. Many laboratories offer a mini panel that hits the highlights and allows you to see if her organs are functioning normally for a reasonable price.
In some dogs as they age their organ systems don't work as well as they once did, and waste products that their organs usually filter out build up in the blood stream and that affects brain function. They may behave much differently because their brain function isn't normal.
At your girl's age however, and with symptoms that seem to worsen at night, I would be more inclined to believe this is related to "sundowner's syndrome" or beginning senility. Their symptoms often tend to occur at night when they are sleepy and more easily confused. It's dark and if they awake they may not remember where they are or what they are supposed to do. As dogs age, just like people, they tend not to sleep as soundly and as such may wake multiple times a night.
In some cases they are over-tired and cannot fall asleep. It is common for these pups to pace and they may sometimes vocalize or stumble too in their confusion. They can even forget their housebreaking habits as things progress and eliminate in the house.
I recommend leaving a night light on at night to help her orient herself. I'm sure it will help to speak calmly to her as well and resettle her.
Sometimes changing the diet to one high in antioxidents and brain supportive nutrients helps. B/d diet by Hills Prescription Science diet products is an excellent one.
A medication called Anipryl (l-selegilene) can also be very helpful. It increases brain neurotransmitter chemicals.
I would call your veterinarian and describe what you have been noticing. They may be willing to prescribe Anipryl if she has been seen within the past year given her symptoms. If not you can at least purchase the b/d diet from them and see if it helps.
In the meantime you can also try a supplement called Melatonin. This is a naturally found hormone in dogs and people that helps regulate the sleep/wake cycle and is involved in seasonal shedding in dogs.
This is a medication that we do use sometimes in dogs to help them relax and sleep, and in cases that have abnormal shedding patterns related to seasonal light changes or abnormal growth hormone fluctuations. The usual dose in dogs is 2mg to 12mg per dog every 12 to 24 hours. Make sure to give a dose 2 hours before bedtime.
Make sure to read the label and DO NOT use the fast dissolve tablets of Melatonin with xylitol as xylitol is toxic for dogs.
To help calm her I like DAP (dog appeasing pheromone) diffusers or collars very much. This is a synthetic analog of a calming pheromone a nursing bitch produces when nursing. These can be used along with a homeopathic, such as Bach's rescue remedy. This is a drop which can be added to food or water.
If none of this seems to be working antihistamines often have the side effect of making a dog sleepy. If she does not have any history of glaucoma or heart disease you can give Benadryl (diphenhydramine only don't use the combination products with decongestants or acetaminophen as they can be toxic for dogs) at a dose of 1mg to 2mg per pound of body weight or one 25mg capsule per 15 to 25 pounds of body weight orally every 8 hours.
At her age with a likely slower metabolism I would try the lower end of the dosing range first and see what effect it has.
Please let me know if you have any further questions.