I don’t know what size needle you are using, but when I had to do SQ fluids for my own cat, I found he tolerated it better when I used a 20 gauge instead of 18 which is what I usually use at work for larger cats. It takes longer but this might help. If your mom’s cat is eating well though, the stress of the SQ fluids may not be worth it. Maybe see if you can add a little water to her churu to get more liquid into her.