Without more details on what she actually needs in the care area, it is hard to say. If she only needs some "help" and monitoring - the apartment might be fine until she needs more or escalated care.
That's how AL works - you pay for the place and the amenities that they provide - IOW - Room and Board - which includes laundry, housekeeping, meals, etc. At the lowest level, "care" is usually only accompanying, monitoring, giving of medications.
As the care level increases, the more care they get and the pricing goes up depending upon the level and amount.
When you say 24/7 supervision with a private caregiver - that means to me that she is at a FULL care level. And if that is the case, a live-in companion isn't trained to give her full care.
Remember if you are gonna do this, the worker has to be paid - as an employee or at least as a caregiver - that also means that workmans comp insurance and liability coverage is a must. Because if the companion / caregiver gets hurt on the job, there is liability exposure to you or your mom.
Are you thinking that the "companion" is gonna cover 24/7? That's a lot of hours. In most every state, caregivers are licensed by the state. That includes a background check also.
When my mother needed 24/7 care, I found (thanks to the hospice nurse) a great personal care home with 24/7 staffing. She was then 89 years old and she was the youngest of the other (4) ladies being cared for at the facility. I was pleased with her care there and it wasn't too far from me. We were encouraged to visit at any time and the Romanian lady that owned the place cooked great food and often had cookouts on the large covered deck. All the ladies were dressed with hair done, in their respective wheelchairs.
My aunt remained in her own home for care - we found her a couple of licensed caregivers that were a mother/daughter team and they covered the 24/7 between them.
It is expensive but how could it be otherwise -
It's Always Something . . . . Roseanna Roseannadanna