With or without religion, good people can behave well and bad people can do evil; but for good people to do evil — that takes religion.
-Steven Weinberg
I would start by pointing out to her that morality exists independant of any God. Realizing there is no good reason to believe in a deity should no more affect her sense of morality than learning that unicorns aren't real. Morality deals with the results that our actions have on other sentient beings - namely humans. Causing harm is bad. Causing well being is good. Barring a serrious brian disorder like psychopathy, everyone understands and can relate to how other people feel and how our actions might influence them (look up Theory of Mind for more infromation on this).
The Golden Rule, treat people how you want to be treated, is most commenly associated with Jesus. Though he certainly wasn't the first person to say it. Isocrates had said it three-hundred years earlier. And Confucius a further two-hundred years before that. It's been part of every major civilization in history up to the present day. And its a concept we all intuitively understand.
But, more importantly, I would pose the following question to her: Which is more moral - doing something so that you can get a reward? - or doing something because you care about others?
Once a person considers the ramifications of this question it's very easy to see that religion gives people bad reasons to do good things - and often bad reasons to do bad things.
On the other hand, basic empathy gives people good reasons to do good things: Do good things for your family - because you love your family. Do good things for your friends - because you love your friends. Help those in need - because they are in need. Be good for goodness sake and help others for the positive effects it has on yourself and the people around you.
There is no need to choose between living well and doing well to others. For they are the same thing.