Go to have the coffee. But say that you'd rather not mix something that seems casual and friendly like coffee w/ R talk. If she wants to go have coffee, "that would be nice." If she wants to work on thing D, you'd feel more comfortable just meeting somewhere more private and focusing on the matters at hand.
If she really has something important to tell you, putting that off isn't going to help you. She may want to do this in a public setting because she's worried about your reaction. On the other hand, she really may want to just talk and things have gotten awkward enough between you that she doesn't feel comfortable saying so. Instead, the one thing you have in common right now (working through the D) is the excuse.
So, I'd say get on with it. Be prepared for some bad news, but be willing to engage in some friendly banter if that's the way it seems to be going.
Me: 50 W:43 S6, S3 M: 12 yrs. T: 17 M is bad & Not happy Bomb Mar '14 S 5 Feb '15 D Bomb 13 Apr '15 (but "no hurry") DB Coach May '15 Wants proceed on D Aug '15 Starting 1-on-1 negotiations Sept '15