As I hope you know please explain to your mother that if anything she has NOTHING to fear from staffies and the like, they are the VERY LEAST likely to bite a person, they are VERY people friendly!!!

As for a Chi pup...well some very small breeds can be snappy because they are treated as kids or toys and not animals by their owners and tend to be aggressive either out of fear / misplaced protection of the owner or dominance even. And that will be even more likely if at the time they are in the arms of their owner..a pup may also not be very socialised and feel threatened by a "big" person coming so close when they thought they were all safe all cuddled up to their owner...

xx