I don't think she needs that much skill act. She needs survivability.
Raise her skill to lvl5, give her a bit of x1.36 skill act and it should be enough. You want to get her 2 skill buff. Combo Hit and Special evade for all is the best. After that, it's sweet bonus.
Try to get some good retain HP. Skill act and re-act are overated for Zinnia imho. You don't care if she can skill twice per turn if she don't survive more than one. A good Zinnia is a Zinnia alive (and that's why Adlay is broken with her).