If you are married, can you still be maid of honour in a Catholic wedding ceremony?

I know it sounds old fashioned, but strictly speaking you would be referred to as the "matron of honour" if you are married.

Traditionally, a maid of honour is an unmarried woman who serves as the bride's principal attendant. If she is married, the term matron of honour is used. This person is typically a close friend or relative of the bride, chosen for her emotional support and organisational skills in the lead up to the big day. However, these days the distinctions are used interchangeably so you can certainly be married and a maid of honour, if you prefer that title.