Kerry, there are no magic ways, but I had the exact same problem with my
mother in law and we managed to get through it with some clever techniques
we worked out.

If you think about it there are a lot of steps involved in planning to take
a shower.   You need to figure out what to do first, and then next, and what
to wash and how, and then to dry off, and you need to organize yourself with
clean clothes to put on afterwards.   It is VERY confusing to a person with
alzheimers.

Your mom just can't handle sequences of actions anymore, so it isn't her
fault.   She needs to get someone to help her through the whole process.
Make it a nice experience.   What I would do is get my mother in law when
she was taking off her nightie and planning to get dressed in the morning,
because she was ALREADY undressed..... that was half the battle.   I would
tell her "we need to shower first" and no matter how she objected, we urged
her to get in the shower.

We had a shower stall with a little bench and the shower head on a hose,
which made things much easier.   I would put on a longish tee shirt and get
right in the shower with her, and help her every step of the way.   I would
give her a shower puff with soap on it, to keep her hands and attention
occupied.

First thing I would put some shampoo on her head right away.   That way she
would HAVE to wash her hair, because it was already in process.    I also
would direct the water AWAY from her, and get her to approve the water
temperature.   They just don't like to shower.... so her participation was
really important.

I would direct her to first wash this, then that..... while I washed her
hair.   The rest was easy.   I would give her nice fluffy towels to wrap up
in, and I'd comb her hair for her.

In short, we made it sort of a spa type of an experience.   Only in the very
beginning did we have resistance, because she was daunted and confused by
the task.    Once I began helping her to shower it never was a problem
again.

You may need to push her a bit in the beginning, but as long as you insist
nicely and help her along, it will work out OK.    And be sure to catch her
when she is either getting ready for bed, or first getting up in the
morning.   In short, when she is already getting undressed or planning to
dress.

Let us know how it works out for you, ......and don't let her say she will
shower alone.   It just won't get done.