Don’t be too hard on yourself about the incident. It was good that you said something. I think it’s hard to respond to someone who takes the Name of God in vain, for example.
Paragraph 1735 says that a person has reduced or nullified responsibility if they do not have knowledge that some action is a sin. It’s hard to tell if she knew enough although she seems to know something.
It’s out of place to refer to Mary in football, for example, a “Hail Mary” play or pass to be specific.
Maybe that was best to say you were offended by what she said.
I don’t know if you both are old enough to speak about this objectively, for example, to mention that anti-Christian slurs seem to be politically correct, a prejudice that people feel free to indulge in.
People “push” against religious belief, but they resent when you push back. That is a type of “witness” when you do push back. Some people act deeply offended if someone uses the wrong pronoun to refer to them. Teachers walk a very thin line about touchy subjects like this. But, to the point, there is not supposed to be discrimination on the basis of religion. No one should create a hostile environment about this.
If this happens once, you can do what you did and let it go. If it happens repeatedly it might be construed as a form of bullying. But, be careful, what goes around, comes around – so watch your backside if she comes back at you. Christ endured many insults. God says (in scripture) revenge is mine. If someone slights me in some way, I don’t have to get upset because I know that person will get what they deserve (as much as I will, for my faults). But, I have really seen people get paid back (or so it appears to me) in this lifetime. It has happened so often I cannot count the times. – and I’m saying, I didn’t have to lift a finger. I feel sorry for them when it happens.
An alternate response would be to say " Mary, pray for us."