I don't think she's judging by calling it a habit. I think she's just noticing. I think maybe she would like you to think about what it is that makes you decide to choose a date - what happens right before you do that - what is it that stimulates the thought in you that you should look at the calendar and choose a date.
Does that make sense?
Because it sounds like it's a reaction to something.
Is it something in therapy that happens (or doesn't happen).
Is it something outside of therapy that happens (or doesn't happen).
Is it anger, desire for revenge, feeling hopeless, feeling overwhelmed, feeling not heard, feeling alone, etc.
Discovering what this is that makes you go to your calendar can give be very helpful to you, can give you insight into how you react to things that are important to you.
I say this because I believe that suicidal thoughts can be learned from.
And they are just thoughts, that don't require action.
They speak of other things, they say "I hurt *this* much!"
So, if we can notice the process (habit, if you will) of how this happens.. what happens that first turns your thoughts to thoughts of suicide, what is it that feels so painful, so overwhelming. It does not have to be something highly dramatic or severe, it can be just something that is overwhelming at the time and that seems as if there is no way out.

Habit is just a word. It just means there is a repeated pattern, that's all. What's important is what that pattern is and how you can learn from it and grow and feel much better