Now that you realize the dynamic, you have an opportunity to PRACTICE (in your head, or -- even better -- out loud when no one is around to hear you) how you are going to handle it next time she pulls this VERY predictable string.
"Wow, I'm sorry to hear all of that. It certainly wasn't my intent to upset you. Look, I'd love to talk but I've got someplace I've gotta be. Talk more later?"
or, if texting:
"I've decided I'm no longer willing to engage in these text wars with you. If it's important, we can discuss it in person, calmly, and if it's not then this is just a cheeseless tunnel and not a good use of my energy. Gotta run."
