Well this is what I would do; If you are a newly Traditional Catholic and just leaving the novus ordo, where many of your family and friends might still be attending, and they might not even understand yet the difference. Then I would go to my priest and ask for a dispensation to attend. He will instruct you as to how to be polite but not participate. However, we Traditional Catholics cover our head for respect of the Blessed Sacrament, and if the Blessed Sacrament is not in the Church, nor is the child receiving it, I would dress modestly and lady like but not cover my head.
Now on the other hand if you are a long time Traditional Catholic and your close friends and family know your stand, I would not go at all, but I would go to your Traditional Catholic gift store and purchase a suitable gift for the person, something that perhaps might plant seeds. Have it blessed by your true priest, that will help to have something blessed in their household. Perhaps a nice book about the Saints, a rosary etc.