I’m not a rav, so I don’t know if this is in line with Halacha (please ask before doing anything) and I have no experience in Kiruv (not yet anyway 🙁 ) but maybe its possible to build up a little bit at a time. For example if she feels Shabbos is too much, maybe she can keep one part and then add to it over time. The benefit is that mentally it might seem easier and it gives her time to get used to it. Either way, tell her not to stop lighting candles.
Hatzlacha