The issue isn't just that she's disappearing, it's that she's setting a precedent that she doesn't actually want to be a full-time employee. She's not actually

The issue isn't just that she's disappearing, it's that she's setting a precedent that she doesn't actually want to be a full-time employee. She's not actually leaving the company; She expects the company to backfill her position for a month and then return the position to her when she decides to come back. In practice, people are generally quite forgiving and happy to step in to cover for someone who has to leave for family emergencies or a normal vacation. It gets a bit harder when someone has simply decided that they're not working this month. Unless her work can simply stop, this means other employees will have to pick up extra work. They can't hire someone new to backfill because this person will be returning soon. They could hire someone new to add extra capacity to the team, but then why give this person their job back in a month when they return? Why not just give it to someone else who plans to actually work full-time? It's actually a much more challenging logistics problem than it sounds, unless the person really does work in a vacuum on work that can be paused for a month without consequence. The impact extends to the rest of the team's workload.