DO let you know you HAVE a plan. Just tell her you're not yet ready to DISCUSS it.
If she is sincere, she will want to know that you have a Plan, and that YOU seem confident in it, and that you can lead her in it. (not CONTROL, but LEAD).
This is important: DO NOT go "melty man" on her in the next 24 hours, no matter how much you'll want to. No "needy/grabby," no pursuing, no following her around the house like a puppy dog, asking her constantly "are you okay??"
Be KIND, but not overly affectionate. Hugs, not kisses, and not too lingering and be the one to break them.
She's done this to you (left you and then came back) repeatedly before; it's imperative that she see and feel "SOMETHING IS DIFFERENT WITH COMMITTED THIS TIME". "He's not falling for my bullsheet this time, hmmmm...."
Strong . . . loving . . . leading. Pick a favorite movie star or TV character who personifies this for you, and get that image of him in your head.
Update us when you can. I'll be out of pocket this evening from about 5 - 9PM Eastern, but will try to check in on you otherwise.