going back to see my family

Re
My husband is in the navy and I haven't seen my family since last October. Well I'm going to visit them this weekend for two weeks. Last time I was there it was a very stressful time for me. I was 6 months pregnant, I just lost our only car in a flood (hurricane Matthew), my husband was deployed, and no body was willing to help me get a new car without a Power Of Attorney from my husband. (It took 100 emails, 25 calls to the ombudsman to get in contact with my husband, and 10 calls from my husband from his ship just to get the right Power Of Attorney. We also got the wrong Power of Attorney 10 times.) again I was extremely stressed out and emotional. My niece is 3, and one day she was making me really mad. I don't even really remember why she acted like she did. All I remember was that I upset her and she started hissing like a cat. Yes you read that right. When she's mad she hisses like a cat, and pretends to scratch at you. When she's happy she barks likes a dog. Well she's been doing that for that past few days I've been with her, and it was soooo frustrating. Well that day I almost spanked her. I didn't! But I almost did. I have never spanked her before, and never had the urge to do it till then. I have felt horrible since the incident, and I'm trying to figure out a way to apologize to my brother for coming extremely close to spanking his daughter. Any advice? (I'm not sure if they believe in spanking their child) (I also feel horrible because she's not my child to spank)