Girlfriend gets angry when boyfriend spends $10K on his 9-year-old dog's surgery instead of assisting her sister with her rent: 'You’d spend ten grand on a dog but you won’t even help my sister keep a roof over her head?'

When you marry someone, you have to accept the presence of their crazy family, but that doesn't mean you have to support them through all of their horrible financial decisions. At the end of the day, your sister-in-law is not your responsibility, and you should not be paying her bills if she is fully capable of doing it herself. 

There are ways to support your family during tough times without enabling them. You shouldn't just give cash to your family unless you're okay with that cash going to something that you don't approve of in the slightest. If you give people financial gifts, you don't have any control over what they do with them. Helping a family member with tasks like grocery shopping or house cleaning is often more meaningful than giving them financial gifts, as you know your act of service is making a tangible positive difference in their lives.