How do you help a parent deal with loneliness?

old. This day in time where everyone lives longer, 63 is deffiently not old!

It is very lonely living alone..

Is there a reason she can not move in with you?

Can she have a Roommate?

If not, can she move somewhere where she can?

Is she able to spend a night with you once a week to give her something to look forward to?

Dones she still drive her own car or does she just sit at home all day?

Have you considered getting her an emotional help Pet?

Does she have any other Family Members, Friends, Church Members, that could visit her, maybe have it scheduled where she would get a visitor every day?

Does she have a Hobbie...plenty to keep her occupied and entertained?
like puzzles, paint by number, coloring, beads for making jewelry, knitting or crocheting, reading material?

Dones she have a computer to keep in touch with people or to just occupy her time or make friends on Facebook, ect?

Does she go to Church where she can make some nice friends and have others to talk to?

When is the last time she's been on even a mini vacation?

Is she capable of signing up and going on a vacation for Singles Only?

Seach for a Senior Group where the Spouse has died or just a Senior Singles Group that she can join.

What about Volunteer work?

Prayers

One thought that came to me is she is still grieving and with the social distancing, closing of community groups, restaurants, movie theaters and all the rest of the things that we would do when we got together with friends.
This makes the isolation even worse.
If everything checks out health wise it may be possible that she needs something to do, something to give her purpose. I think continuing with counseling is a good idea. If there is a place where she can volunteer or better yet if she can get a part time job (keeping safety in mind) that might make her feel better.
My Husband died in 2016 and if I did not have my Volunteer activities and friends that I bolster and they bolster me I would go crazy. I do have my daughter (step daughter actually..but I hate that "step" term) and grand kids that I am with a lot.
All that activity helps tremendously.
She might even want to take a course or two at the local community college. Many can be done on line.
(by the way get thyroid checked out and vitamin D)

You don't mention if you live local to your mom. Even if you don't I think her behavior warrants a physical exam by her doctor. She may be exhibiting symptoms of a UTI, especially if this behavior seems like a sudden change. UTIs in the elderly are extremely common and frequent (often not completely related to hygiene) and often have no other symptoms than personality, behavior or cognitive changes. She is probably not even experiencing pain when urinating (yet) or is cognizant of any urgency. This can be cleared up with antibiotics.

Then her hand-washing due to "bugs"...this does not seem like the typical OCD behavior because she is thinking or seeing bugs. Typical OCD is driven by mental/inner messages, not because they are imagining bugs. Is your mom on any medication? It is possible she may be over- or under-dosing. Doc also needs to verify this.

It is possible that your dad was "covering" for your mom's deficits or decline and you are now seeing it for what it is. Again, there are many possibilities and you will need to sleuth it out and NOT take her word for it -- this requires a visit of at least a week (if you are not local).

If you don't live close to her I think you or a trusted family member (and preferably someone with her medical PoA) take her to the doctor and figure out what is going on. It may be more than grief. She is too young to have dementia. I wish you all the best as you begin to help her and peace in your heart.