Chihuahuas usually don't do well in cold weather, and that's why many people buy clothes for their chihuahuas. If your dog shivers - its too cold. Generally, in the house she'll be fine, as long as its reasonably heated, if you go out its best to get a jacket for her.
Sometimes it’s simply too cold for pets to be outside, regardless of their breed. Prolonged exposure to dangerously cold temperatures can put pets in danger of frostbite and hypothermia, which occurs when the body is no longer able to sustain normal temperature. Symptoms of hypothermia in pets range from weakness and shivering to inaudible heartbeat and trouble breathing, depending on severity.