Am I overthinking

My wife (32) and I (39) have 3 kids together and I have daughter from a previous marriage. When we first got together she treated my daughter like her own and they were besties. After we had our own kids together she slowly changed and started treating my daughter differently. Most recently she put up Christmas stockings and she put then in age order except for my daughter who is the oldest at the end. I asked why she want the first on next to us since it's usually age order. She immediately threw a tantrum and finally popped off that she isn't her oldest. I then moved my daughter next to my stocking since she is my oldest. She moved it back.and says that's how theybare gonna be and I can get over it. We have had this argument before and my daughter even mentioned it. Am I making it a bigger deal than it is or should I hold my ground. My kids are 14F, 8M, 5M, and 2F.