Meaning:

“流水线” means “production line,” and “公主” is “a princess.” “Production-line princesses,” a popular spectacle on WeChat Moments during this May Day holiday, refers to young women dressed up as princesses from various ethnic groups posing for photos at such tourist destinations as Xishuangbanna and the Korean Ethnic Park of Yanji. Dressed in similar costumes and wearing similar makeup and accessories unique to Korean, Dai or Tibetan ethnic groups, these young women look quite alike, earning themselves the nickname “production-line princesses.”

Example:

A: 你看到丽丽发在朋友圈的照片了吗？

Nǐ kàndào lìlì fā zài péngyǒuquān de zhào piān le ma？

Did you see the photos Li Li posted on her WeChat Moments?

B: 看到了。又一个流水线公主。

Kàndào le。Yòu yīge liúshuǐxiàn gōngzhǔ。

I did. She’s just another woman dressed up as a cookie-cutter ethnic minority group princess.