ANSWER:

Refrain from responding. 

QUESTION: Shaykh, one of my Mahrams (sufi) who celebrates the Mawlid sent me a message – “Rabi Al Awwal Mubaarak” Is it ok if I reply خَيرْ مُبارك as in our culture for replying to such greetings (wedding mubarak, etc) Or do I refrain in case she may send me a message on the Mawlid?