Well that's a hard question to answer, but I'll try my best. Let's look at it in two ways.
Is there a general story all planned out? Yes. It's not really written down, but there is a plot I am following with a beginning, middle and end. Some of these ideas are from as far back as 2001; infact, Chapter 4 is going to be based around what was once going to be a "fanarc" for Namir Deiter, back when Mrs. Marks had just a couple of comics and still accepted fan submissions.
What about each individual strip? It depends. If I'm having trouble with it and I do strike upon an idea that works, I'll try to jot it down. But individual strips dialogues and such are very rarely written down separately ahead of time, unless I'm brainstorming with other artists.
So, the answer is "kinda".