Is it OK to hide mom's old slippers and replace with gripper slippers?

No, you are not wrong, because you are doing this to protect her.

I hate slippers or fuzzy socks that have those grippers on the bottom. I find myself almost tripping because the slippers or socks would grab the carpet or floor, lurching me forward. In the trash they went. I just put on regular shoes first thing in the morning, that have arch supports, to wear around the house.

wHY NOT REPLACE THEM WITH NEW ONES THAT LOOK JUST LIKE THE OLD ONES?

I see that the deed is done but but I want to offer a different perspective because it's not always so black and white. Everyone is on the side of "get rid of the slippers" but unless the slippers are dirty, worn out, high heeled or have extra slippery soles they are probably not a problem. I'm fussy about what goes on my feet and select for comfort over everything else, presenting me with slippers that are "better" is not going to make me happy. Plus grippy soles can change the way you walk and in people who tend to shuffle can actually cause stumbles.

You are not wrong. Change out the slippers and she may never notice. If she does, change the subject. She may forget about it.

So I took my mom's slippers away. Needless to say she's not happy about it and doesn't want to see me anymore. I assume that lasts about a day or two. It had to be done. I made an off color joke about it to the aid. What else can you do?

Nope, you should decide. Throw them out in such a way she cannot retrieve them and get grippers.

I threw my alzheimer's mom's favorite (disgusting fall hazard) slippers in the trash and she fished them back out and kept wearing them. You might have to take them home and toss them there. Why not? Just make sure she has a replacement pair.

Hide them? Just throw them out or donate them if they're clean and in lightly used. If she balks at the new ones tell her the doctor said this is the kind she needs to wear for her own safety.

No you are not wrong.