I'd leave her to work through her feelings the way she wants to. Being heartbroken about the end of a romance seems very normal and healthy to me. Maybe if we're talking 4, 6, 8 weeks of mourning, I'd be worried. But if my kids were all chipper and it mean nothing to her early on, I'd actually be more concerned.
The reason I say that is because my mom was very intolerant of my feelings- make that everyone's, actually- so I was super cautious about that with my kids. My mom got to have the full range of emotions, but everyone else in the family was supposed to be this way or that way, and that was decided by her. Anything other than happy and "normal"- by her yardstick- caused her discomfort. I'd try to just keep living the way you live and tend to your stuff as you usually do, and let her be sad.