Recently (2 months ago) added a young male beagle to the household, our existing dog (female corgi/lab mix) had been with us about a year. She was always a little timid with other dogs - the dog park was never very pleasant for her, but she did okay meeting other dogs one-on-one when out walking.
Now, with the new puppy she is fine, and clearly the Alpha dog, but all of a sudden is VERY scared of non-family dogs - to the point that, if we're out walking and she hears a dog barking, she will dig in her heels and refuse to keep walking. Is there any explanation for this, or a way to help her get over it?

