"I'm planning on taking a vacation from DD/MM to DD'/MM'. Are there any conflicts in the lab for that time period?". If the answer is no, she can put it on the

"I'm planning on taking a vacation from DD/MM to DD'/MM'. Are there any conflicts in the lab for that time period?". If the answer is no, she can put it on the shared calendar and have her mind at peace. If he says yes, then you can move the vacation to before/after the conflicts. (If the PI is formally opposed to any vacation, then it's a larger problem) I used to be a PhD student (although I dropped out), so I know the ironies of academia too well. But for situations like this, clear communication in advance solves 99% of problems (and this is not specific to academia).