My sister in law has just blown up?

My brother and sister in law live with me and my mother temporarily before moving into their new house. Earlier today, I went on a walk with them and their 2 dogs. I was holding onto one of their leads. My brother and sister in law don’t like the dogs to have a sniff before we get to a field and if they stop for a little sniff they drag them by the lead to get them to walk. The dog I was holding stopped for a little sniff and my sister in law said ‘ Just pull him Katie’, in a really nasty tone. I felt offended and walked back home. Just when they came back, I decided to go on a walk to cool down and just get some exercise in general. When I got back, my mother told me that and she got into a massive argument with her. It started off by her asking ‘where is Katie?’. Then my mom told her that I’m abit upset by the way she spoke to me. Apparently it all spiralled from there, my sister in law went mental , started shaking, saying she won’t apologise and that my mom should let me speak. She was really angry and her and my brother are out now. I honestly didn’t think it would get so out of hand. I thought maybe I’d just be be annoyed for a few days then we’d get back to normal and I didn’t think my mom would mention it. What do you guys think?
My sister in law has just blown up?
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