Not sure how it works in other countries but for getting vaccines in Japan, you get some mail that gets you to choose whether you want to schedule an appointment yourself, let the schedule be decided for you, or opt out of it.
She probably opted to be scheduled instead of making her own, which caused the unfortunate timing. Combine that with underestimating the side effects and yeah
On the other hand, if she actually specifically set it up to avoid the collab, I would actually be impressed because that's some next level effort lol