Actually, The whole saying is 'blood of the covenant is thicker than water of the womb', as in the people you choose as your family are more important than those you are given as a family. So, No, it applies to anyone you choose to be your family. OP was using it right.

Sell the cute lil thing, than tell her it left her.

Tell your parents about this. I'm sure that your sister will not mind not being in their will. After all, the dog is now her only family. She can inherit its belongings when it dies.

If she was your sister, why wouldn't she know you are extremely allergic to dogs. And even if she did but just didn't care, that makes her a huge bitch that obviously doesn't care about other peoples issues which confuses me, why would you be roommates with her?

leave. dogs are cute.

Sounds like her way of booting you out for whatever reason. In any case, I'd move, myself. Wouldn't want to live w/ someone, sister or not, who pulled that stunt.

Just have someone kill the dog for you... Problem solved

Ask her when her and the dog served in battle together. She is half right "blood is thicker than water" is an old saying that means the blood you shed with your fellow soldiers is thicker and more bonding than the amniotic fluid you and your siblings shared.

You should buy gloves and a protective suit, and offset the cost buy selling the dog to your local Chinese restaurant.

The good news is that you're the smart sister!