Why is she against a joint grief program such that she will have "kicking and screaming" objections? What other sources of support does she have now, and could she have instead of this joint program? What would she propose to do instead?

Forcing people into a form of therapy is risky, and forcing kids to do intensely personal projects such as therapy with a parent is also risky. My suggestion is to be sure that you've sufficiently considered her objections, as well as options she could do on her own, such as a grief support group for teenagers.