Let me see if I can help here. Thanks to our mayor for the headsup.

I currently have two Chihuahuas, Daisy and Delilah. They are preceded by my longhaired Chi, Killer. I used to be just like your Mom. I sterotyped Chis as biters, yappers, etc.

Now, I say, once you get to know a Chihuahua, you will know what it's like to love a Chihuahua. Not all Chis are sweethearts and some are nippers, yappers, etc. However, they can be trained. They're smart little doggies. Sometimes they're a little stubborn but most of the time, they're very trainable.

My girls are sweethearts. They don't nip unless they're threatened and that's rare. I think Delliah nipped someone one time and it was a vet tech that startled her. Daisy doesn't try to nip anybody. They're very much attached to humans and must have human contact. They like to sleep under the covers with you and Chis are known burrowers.
They can be socialized with no problem. If not, they can become territorial.

Like any other breed, they need training and love. They're not perfect. No dog is perfect. If they start to nip, bite , or act mean(after proper training), get them to the vet. There may be a medical condition. I really feel there could almost always be a medical condition to cause this type of behavior. If not medical, there could be something in their past that triggers bad behavior. If you put quality time into raising the doggie, you will be a happy person.

Best of luck to you in convincing your Mom. Keep us posted!

To add: My Daisy loves being picked up so I hope you don't mind that.