I still live at home. When I got my Yorkie - my mom's cats HATED her, but they are now tolerating her and realize that she's there to stay.
Your mom's cat is probably just offended that there is another animal there (who I would assume is getting a TON of attention more than the cat, hey - no shame in that - I'm the same way...)...
My little yorkie goes after the cats and it is HILARIOUS!
I yell at the cats when they swipe at her and they've learned to tolerate her. Both are females and aren't fixed...
I really think it's a time thing - We've always had two cats, when one would pass we'd get another - the old cat usually took a few months to adjust but would eventually love the new kitty...
I'm sure it will be the same with her pupp, she's SO excited about the kitty but the kitty is jealous/upset... give it time
Keep me updated!