AITA for telling my SIL that I did not have eight hundred dollars in cash sitting around to lend her?

I had to take care of my niece last weekend since my SIL was out of town. I did not mind at all but as my husband and I were saying good bye to my SIL and niece she asked if my husband could drive my niece back home a week later. She mentioned that the transportation she had lined up for her has cancelled. I said I could do it. My husband was busy, so I offered to drive back my niece. My SIL said she would cover gas so I got in my car and drove there to get my niece. <br><br>After a while I was starting to get a bit low on gas so I pulled over at a gas station to fill up. Before I did I called my SIL to let her know my location and to ask her how she was going to pay me back. I figured she would send the money via paypal or some other app. Instead she said that my niece was supposed to bring back the money for gas. I was flabbergasted. I asked her how she thought my niece was going to carry almost eight hundred in cash. She said she had given my niece the money before she left her house. I asked where my niece was carrying that money and my SIL admitted that she had left the money at home after she packed her suitcase.<br><br>I was so annoyed that I told her I was out of pocket almost eight hundred and she had no call to send my niece without the money. She said she was going through a tough time. I told her all of us were going through a tough time. I am not rich but I am not poor either. Still close to eight hundred is a lot to most people and I felt like she was seriously irresponsible to send her daughter without the money to pay me back after I have spent my entire Saturday taking care of her daughter. <br><br>She argued that I made that money doing nothing and all I had to do was drive her daughter home. I told her that was another AH thing to say since I was giving my time but the gas did have to be paid for. She argued and I got tired and told her I was going to consider her loaning me money and to pay me back when she could as I did not want to keep talking about money. <br><br>She started complaining to the family and some of them are on her side. They said she did not have the money and could not afford to pay me back but that I was in a better position to pay for the gas than she was. Some said I was being petty and AH for not helping my family members out. I asked my husband if it made me AH for not letting them feel comfortable borrowing without paying me back. He said I was NTA and if I let them feel like I was their personal atm they would do it more often.