She has a history of pushing her faith on others, which is probably why she asked (to bring the subject up), rather than just quietly getting on with it without anyone knowing.
Over xmas, I was asked by my neighbour if I'd like to go to church with her. I'd rather she hadn't.
Why?
It puts non-xians in an awkward position because while it is normally the case that declining such an offer and exposing a lack of religion has no negative ramifications, it is often the case that it results in offence. To some it's ok to express their religion (because it's the "true" one) but not ok for others to express different beliefs.
Just look at the death threats David Attenborough has recieved simply for not crediting the xian god in his nature programs.