What is the best thing I can say to Mom who is devastated that her favorite caregiver may be losing her job?

I notice that you say, "May be leaving". Is this a certainty? If this person has let you know this may be happening, has she told you the reason(s)?

I'm aware that many individuals change companies because there are often sign-on bonuses involved. If this is the case, I doubt she'll change her mind.

There may be a number of reason she "may be leaving". Scheduling conflicts,
increasing or decreasing the number of hours she works, personality conflicts that have developed, problems at home, health reasons, etc.

Perhaps she is waiting to see if the administration is willing to work with her to resolve whatever is/are the issues.

As for letting all of you know that she "may be leaving" - it may be because she feels it would be more devastating for your mom if she were suddenly be gone without saying anything & that is a possibility.

If she doesn't tell you "the why or whys"

It's possible she may have ulterior agenda.

Perhaps she needs a letter of praise for her personnel file. However, from what you tell me, I can't imagine she would hesitate to ask for one. If you do write one for her, make sure you list all the various ways she has gone above & beyond compared to other people in the same position do. But it's important not to mention anything that could possibly get her in trouble because it's against policy. You will need to check with her (& show her this letter) before sending it IF THIS is something she needs &/or you decide to do.

If you suspect there's something "off" about her telling you she "may be leaving", perhaps you might want to do a background check on her.

It all boils down to a judgment call on your part.

There were "regulars" who took care of my mother when she was in AL who let her know they were leaving because they knew she would be upset if they were just suddenly gone. Each time, it saddened her but she understood. Sometimes it was harder on her than other times - because of the bond she'd formed with the person.

Accidently posted my answer twice; so, I deleted one of them.

Imho, it would be best to focus on the positives in this situation. - maybe your mother could still see this caregiver at some point.

I'd be wondering what the reason is for her losing her job. Who loses a job during this insane pandemic? It's hard to find good people! Unless she is leaving of her own choice. If the relationship is that good in both directions there is nothing really keeping this caregiver, if she wishes, from keeping in touch. If she's losing her job are you able to hire her privately then?

I would try to explain to your mom that the caregiver had some issues come up that she can no longer be in that position of caregiving (something like she has to move and won't be in that area anymore).  my father liked a caregiver that was coming to the house (he had beginnings or middle of dementia), but we think that he must have either said something to her or maybe touched her wrong, but she requested to no longer come out to the house.  We asked what happened and they wouldn't say so dad would be constantly asking for her.  I explained that she got another job and that she no longer would be coming out.  We apologized to the place that hired that lady even though we never found out what happened.  Wishing you luck.

Better to focus on telling this woman how much you appreciated her work and to wish her well if she leaves for other employment.

I'd focus on the positive. I've seen a lot of firings, layoffs in my day and I've seen people voluntarily leave employment for a multitude of reasons as well. If this employee were being let go for a performance-based concern, she would be gone already from my experience. Sometimes non-performance based layoffs are quick and sudden as well - you'd arrive at the facility and beloved caregiver would just be gone. So you could tell your mom that her favorite caregiver did a great job overall and is more than likely just moving on to be a blessing to someone else. I once told my child (when a favorite teacher left the school) that she needed to be grateful their paths ever crossed in the first place and not think so much about what will never be. I think that applies here as well. Do be careful with asking questions about this situation. I have found that some organizations prohibit employees from discussing their separation from the company, so please be aware of that possibility. And, some employees who are leaving voluntarily may also choose to play their cards carefully and not discuss personal details with others. In either case, I think it's always helpful and kind to send a letter of appreciation - but I'd keep the letter's content pertaining only to your mom's care and not comment on the caregiver leaving or the situation surrounding her leaving.

You might try reminding mom about all the people who change jobs, quit, are laid off etc. all the time. Maybe even her husband or herself had to change jobs at some point in life. She may be more receptive to the change if she looks at it through the caregiver's eyes.

Maybe if the woman actually leaves, you could pay her a couple hrs once a week to visit and be your mom's companion.

Sad but better that your mom has her mind so she'll be able to understand the Caregiver has to leave but tell her that they'll hire another nice person.

Do you know why she may be loosing her job?
Odd at this time when caregivers are necessary that they would be letting her at this time is strange. (Unless she has been there a while and they can let 1 higher paid worker go and hire 2 inexperienced people for the same $$)
I would send a note to the facility letting them know that you are sad to hear of "Betty Jean" leaving and include a note as to how much you appreciate the job she has done and if there is any way that they would reconsider letting this person go.
I would also send a letter to the employee "Betty Jean" and tell her the same thing and she can use the letter when looking for another job. (It is also possible that she already has a job and it is she that gave notice)

With good planning the current caregiver will "break in" another as to each residents needs, and "quirks" and that would make the transition easier.
I am sure mom is used to others as this 1 person is not there 24/7/365.

Does Mom have money to hire her a few hours a day? Will the AL allow it?

If this is possible, than the bill for Moms care should be adjusted if this aide does the work. Lets say she bathes Mom, then Mom should not be charged for that in her care plan.