What is the ruling on a girl working in a shop that sells women's lingerie, while she works with another girl in the same shop?

There is no objection to employing a girl in a shop if it does not lead to her intermingling with men. The work of women in these shops is more appropriate because most of their customers are women. If circumstances necessitate dealing with a man, then the Sharia guidelines must be adhered to, such as covering the 'awrah (intimate parts), limiting speech to what is necessary, not softening the voice, and avoiding privacy (khalwa).