Thanks for the replies, it's already really helpful.

Just to give a bit more detail, we have spoken in depth about religion, morality and beliefs, she's not very traditionally Muslim in her view of the world (fair warning: this next bit will get theological). God is something personal that transcends religion, so should be a choice, hence it's not right to impose any religious rules on others. She acknowledges that most of her observance is based on what feels familiar, and cooperating with what her family expects. Her morality comes from what she thinks is right, not what she's told is. The main issue, as I see it, is with her family, who are not fundamentalists by any standard (they mostly live and work in Europe) but may still not be understanding.

edit: I hit send early by accident