because she doesn't remember.  if i were you, i would simply
establish a certain day or days each week that you will have an
evening caregiver, tell her that's the schedule, and stick to it.
you might try having her there in the evening when you're around
once before you go out again, to try to establish the caregiver
comes evenings now as well as days.

i know that it's hard to parent your parent, especially one
that's always been in charge, but you need to take charge so that
you can stay mentally and physically healthy enough to keep on
caring for her.

as the oldest son, i had a much easier job getting my mother to
do things she didn't want to do than my siblings, who usually
avoided any kind of conflict.  i was partly able to do that by
adopting the demeanor my father used when dealing with me as an
unruly teenager --- implacable calm, matter of factly saying that
you WILL do this now.

part of the problem as AD folks regress is that if they were
selfish at all they get more selfish and self-centered, like
younger and younger kids, and my mother was sometimes behaving
like a rebellious teen.  i learned to simply just ignore it and
do whatever i had to do to keep her safe and me sane, even when
she complained to my sibs that i was trying to run her life
(keeping her on her med schedule, making sure she could no longer
drive when unsafe, going to the doctor with her so someone would
remember what her doc said).

I say you should live your life and never mind about the fuss.   She did
forget it the next morning didn't she?

A trick you could try is to put her to bed a little earlier and go out a
little later, so she is unaware you have left.   Early in the game, Ida
couldn't understand why there was someone left with her when we had to go
out either.  My next door neighbor was our "granny-sitter" and since she
dropped by here from time to time, her face was somewhat familiar, and she
imagined that she was just there for a visit.   We needed our very rare
times out of the house, and I didn't care if she made a fuss.

One other thing I would like to say, and I hope I can say it without
sounding too crass.   Over the course of several years, and given the nature
of the illness, naturally from time to time there were some stressful
moments.   We RELIED on the fact that it was all forgotten the next morning.
There were times I was very grateful that it was forgotten the next morning.
Evenings, for people with alzheimers, are KNOWN to be stressful with what is
called "sundowning"....  But in the morning she was as sweet as could be,
with a nice smile.... almost innocent like a child.   Every day was a brand
new start.