As someone that works with rescue I see it too many times. Younger girl gets a small dog, loves the dog just like a baby, then has a human baby. Next thing, the dog is too much trouble, takes to much time and they are rehoming the dog.
Forrest one of my current fosters is a perfect example of this. She advertised him on Craigslist. I see the ads almost everyday on CL - same circumstances
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But, then I know of other girls that although their dog gets less attention, they do keep their dogs and still love them.