Q: Can laymen and women wear choir dress? Can they wear cassock and surplice at mass?
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A: There is no prohibition for women wearing cassock and surplice. It’s not accurate to call that “choir dress”. That is an expression used in reference to the attire of priests who attend mass without concelebrating. Cassock and surplice may be worn by laymen and women, and the practice is observed in many churches throughout the world.
Legislation can be found in GIRM 119b and 339. You can also go here http://www.vatican.va/roman_curia/pontifical_councils/laity/documents/rc_con_interdic_doc_15081997_en.html and read Article 6.
Servers wear “appropriate and dignified clothing” (339) and “lawfully approved attire” (119b). The footnote to 119b is to Article 6 of the document I’ve cited above. It forbids lay ministers to wear “stoles, chasubles and dalmatics.” It does not forbid cassock and surplice.