A lot of female dogs get very stressed out by the sounds of peeping and squealing because they instinctively want to care for puppies when they whine and cry. So maybe the peeping is telling her these are babies that need care.
I've heard a lot of stories about female dogs that 'mother' their squeaky toys and become distressed when they accidentally make one squeak!
Of course, not all female dogs are like that...mine tears the squeakers out of her toys and pops them. She won't be meeting my chicks.