Weird and low tone meowing
Thanks for reaching out to us. I’m sorry to hear that your tux cat isn’t acting herself.
I would be concerned about stress with that sort of meow but you’re right to book a veterinary appointment first to rule out pain or underlying illness. Is she still eating and drinking, peeing and pooping as normal? Can she meow normally or does her normal meow also sound different?
If she’s still eating, drinking, peeing and pooping as normal then Saturday should be fine unless she develops other symptoms before then or seems distressed. Your vet will examine her fully and run any tests if necessary.
After you’ve ruled out illness or pain at your veterinary visit, I would focus on stress as the cause. She’s likely feeling threatened and maybe a bit territorial with the new kitten in the house. Even though they seem to be getting on well, I would ensure that both cats have separate eating and drinking areas, litter areas (and plenty of them, rule of thumb is 1 per cat plus one extra), plenty of hiding areas and areas to escape from each other. It’s also important to divide your time between them equally. Plug in synthetic pheromones can be very helpful in this situation.
We have some more information here on introducing cats and ensuring everything goes smoothly.
I hope that helps and that Tux is feeling back to herself soon,