It sounds like your dog is dealing with some cognitive dysfunction.
Some older dogs get a little anxious at night for reasons we really don't understand. At our clinic we refer to it as 'sundowning', where the animal is fine all day, but then becomes restless and agitated at night. Obviously, your dog is more disorientated in the evenings, which makes me reasonably sure that's what is going on.
Some vets refer to it as geriatric cognitive dysfunction, and you can find more information here:
Something you could consider would be talking to your vet about a light sedative for your pup in the evenings. One that we use is called Clomicalm and really seems to work well to keep this issue under control.
Another option would be something to help with the anxiety that doesn't have to be ingested (eaten), so it wouldn't interfere with the other medications she may be on at some point. I love using the DAP collar:
These are collars that are impregnated with a man-made version of the dog appeasing pheromone, which is a pheromone that nursing bitches give off to their pups to help them feel calm and secure. It's something that humans can't smell, but it has an amazing effect on dogs with anxiety and other issues. Although you can find them at your vet's office..you can also find them online at places like Amazon.com and Ebay for much cheaper. Just make sure they're DAP brand, as they seem to work better than some other versions.
I've used the DAP collar in my own dogs and with some of the dogs I've rehabilitated and I really, really like the results. Just keep in mind that the collar only lasts for 30 days, so you'll have to replace it monthly if it works for you.
I hope this helps.