I wouldn't be at all shocked if she knew the pup was a girl the whole time and has had Cookie picked out for ages. She probably thought if she pretended she wanted a male dog then we wouldn't say she wanted to breed puppies again. I thought it was weird she used up her boy name when they apparently aren't preventing and could POSSIBLY have another child.
These people have bred puppies before, surely SOMEONE in that house would've seen the dog had no willy before now? And if the pup has been known as Arlo this whole time then why would Sue be so set on changing the name when Arlo is fairly unisex? She made up that story about wanting to swap for a boy pup to make it seem like she really wanted a boy. Instead it just made her look dumb for being unable to tell the difference despite breeding dogs before. And it made her look heartless for being willing to swap dogs, proving she hadn't bonded with Cookie enough to want to keep her. AND it made her look clueless for bringing a male puppy into her pack of probably unspayed female dogs.
Cookie is still a better name than Ayprill or Narlah
Sophie is a better mum than Sue but I can't get over poor Ayprills name