Am I right to feel guilty about last night's "incident"?

Instant flashback to my mom slamming on the brakes and her right arm coming straight across my face/body to stop my possible flying into the windshield.
Just a protective reflex on your part. She’s probably not teachable at this point but your reaction was appropriate. Possibly a combo of fear, annoyance and love.

edit. But if it made you feel bad, maybe next time wait until she’s in bed.

No harm, no foul. No guilt required.

No guilt is needed. I would have done the same thing. She could have fallen.

You kept mom from possibly falling on a wet floor. You'd do the same for ANYONE at any age.

No, no guilt required at all!!

You wouldn't feel guilty if the person was a toddler and had limited ability to understand the situation, so no, do not feel guilty!

You wrote back in Feb 2021 that you were considering taking a month off from the caregiving duties. Did you? Was help hired? Or are you still the only one?

I know that feeling and it burns deep down when you realise the action isn't representative of the indiscretion. Of course, safety is one justification for response without hesitation - you may have felt she could slip, or might have been taken by surprise with the sudden distraction from your chore. Also, when you are preoccupied, it is helpful to know they are somewhere specifically and not wandering around being a risk to themselves.

My dad tends to sulk when redirected from a fixation or irrational objective, so the reduced cooperation may relate to feeling deprived more than any physical injury.
I would be more concerned if you didn't feel any pangs of remorse, so your acknowledgement will serve you well next time.
Your duty of care includes being the one to say no or intervening in certain behaviours that may be detrimental to their well being, as the capacity for judgement is often flawed.
At the same time, remembering their frailty can foster empathy for how hard it must be for them also to navigate what we often take for granted.

There is no reason to feel guilty. If she still had her mind and was sane, she would have stayed out of your way so you could clean the floor. However, she is now like a child and so she has to be told or made to do things that are necessary.

Your goal should not be to keep her happy at all cost because that cost will be very dear.