She has been working herself too hard. Burning the candles at both ends so to speak.
I think she did not really want to take on the Oil case but did so thinking she would need the money to make up for Jimmy being suspended for the year.
You have signs of what was going to happen.
Her Being tired.
When she was going to meet Mesa Verda people she set her phone for a five minute nap and as soon as she closed her eyes it went off.
When she was running behind and jimmy kept asking her questions...what people might have missed or forgot was that her coffee mug was empty and she asked to have it refilled but I don't think she ever did as she was in such a hurry.
I thought it was silly how she got stuck in the sand while talking to the oil guy but I think that was just another setup to make it so her tires were going bad or bald.
Her doing a repetitious mantra of how she would open the meeting or start off the meeting could also be a form of self hypnosis to someone really tired and repeating themselves.
I imagine they will show her falling asleep driving next week only to have her wake up, her tires not grip well enough and her running off the road.
I am also guessing that Jimmy does something else that added with the pressure he has already caused her, pushes her to leave him for good. He gets his money from sandpiper and buys his property in the strip mall and sets it up while waiting to practice law again.