Home Health Aide just stopped showing up- could it be theft?

This kind of thing happens often with in-home caregiving. True, she should have told you that she was quitting your mother. It's also unlikely that the reason for her ghosting you is theft.
All hired caregivers (private or agency) know how our line of work operates. We all know that any one of us can be dismissed for no reason at all. That we will be kicked off an assignment without warning if cheaper help is found. We also know that families and agency bosses will look us right in the eye and tell us what a wonderful job we're doing while sticking the knife in our backs at the same time.
The most likely reason the aide ghosted your mother is because she found a better position and wanted to make sure it was solid before actually quitting her previous one.
Employers do the same thing.
On my last job (I had been with this client over 4 years) her son decided that myself and the night aide were going to get two weeks off (without pay of course) over the Christmas holiday.
This sounded great because in almost five years of service with the client, I had all of one week off (without pay) because I was able to arrange respite care for her in a nursing home.
The son claimed he was giving us a respite break and was bringing a respite live-in to take care of his mother so we could have a couple weeks off. Then we were to return after the new year.
This wasn't true. The two week break was to give the "temporary" respite live-in a chance and to make sure she worked out. So, he didn't fire us outright and tell us we were being replaced. He kept us thinking we were returning after the new year just in case this new one he hired didn't work out.
Then after almost five years of exceptional service to his invalid mother and father, I got a text saying 'my services are no longer needed'.
Your mom ghosted because your caregiver knows how it works and was making sure she didn't lose. Personally, I would have told you I was going, must most won't.
Most employers won't tell their regulars when they're being dismissed either.

Honestly, my first thought was she found a different client that was better for her - more pay, closer to home, less work, something along those lines - and just didn't have the courtesy to let you know. Or maybe she's still trying to judge which job is "better" and is hedging her bets by not formally resigning. Either way, if she's not reliable, then she's really not a good fit for you, because one of the major reasons you look for a home health aide is to make you life less stressful, not more so.

I didn't think theft right off the bat, either; especially since you haven't noticed anything of real value missing.

I hope you can find reliable help soon! Good luck.

We are, I suspect, in the same position you are. We can only "guess". It is, if nothing else, a lesson in acting early when there is evidence of someone not being reliable. I wish you better luck with next person hired. Try to get really good references and check them.

As a family, we NEVER had good luck with agency help OR private hire help. We would up paying friends of the family when fill in respite care was necessary.

Unsure about theft.. until something is found to be missing but totally unprofessional.

Ensure you have terminated her contract & have everything in writing (keep all texts & emails) as future recourse just in case any future issues.

Any meds missing by chance?

It is a strange world we're a living in. Looking for staff at work, people do not show up for interviews. Once offered the job, they accept, then do not show up or even call. Strange things going on everywhere.

I wouldn't think theft either.