When a non-Muslim joins the fast

As-salamu alaykum! I'd really appreciate some thoughts on this. My manager at work has decided to fast with me for a day next week. I think it's really beautiful that she wants to share this experience, but I'm a bit worried since I know it'll be tougher for her. For us as Muslims, we fast seeking Allah's pleasure and have the spiritual strength that comes with that intention. She doesn't have that same perspective, so when she struggles, I'm not sure what to say. I want to gently explain why fasting matters to us and why it's challenging, but I don't want to overstep or sound preachy. Any advice on how to approach this would be so helpful. Jazakum Allahu khayran!