This might be kinda mean but just flat out tell her all the cons of raising a pup. They chew things, bark a lot, whine contiously (exagerrate a bit. When my friend mentionned she wanted a dog I asked if she was willing to do little things like brush him and she said no. So I exagerrated on everything - they poop a lot, they're expensive...and I convinced her not to get one) Mainly just say things that will turn her off from the idea of a dog.