Between the husband and I, we've been owned by 3 Chihuahua mixes. Mine was Sophie, a 15 year old Chi/Dachshund cross that was dumped on a highway in the summer. I took her home the next day (I worked at the SPCA at the time). She was a sweetie, protective but never nippy. She enjoyed going for walks, was quiet and enjoyed playing a bit. I had her for 2 years until her kidney failed.

Hubby's dogs were Chi/Pom mixes, also rescues. They both were super sweet and playful. The only time they ever nipped was when a teenager pulled an ear or tail (in a hurtful way, not playful).

Our dogs were never carried around or treated like children, and I think that had a lot to do with their attitudes. They didn't have much anxiety in their lives, they knew where they stood in the pack, etc.

Chihuahuas are one of my favorite small breeds, and I am actually on a waiting list with a local rescue to adopt one

Have you tried contacting a local club or breeder? Perhaps if your mom could visit with some good natured dogs she would change her mind? Good luck either way in your quest for a Chi!