我的妹妹英文

当然算了。主语相当于she，典型的第三人称单数！

my sister

这样翻译:my little sister 希望我的回答对你有帮助！

I have a little sister, her 4-year-old a year. She also has short thin, short hair, some yellow, is a very lovely girl.

My sisti

I have a litter sister.She is 4 years old. She is short and thin.She has short hair(有点黄不好说）.She is very lovely！

如果是一个妹妹就是三单，my sister.但是如果是我的妹妹们，超过两个妹妹，就是复数了不少三单。所以看具体情况。