Work related travel with EU blue card (Germany)

Question

I am writing on behalf of my friend. She is an Indian with a valid German Blue Card. Her future role in her current company has to do with meeting clients and her employer wants to know if she is permitted to travel to other European countries (EU-schengen states) for work/ business meetings etc. We know she is allowed to travel freely within EU-schengen states. However, we are not sure about following 3 things:

1. Is she allowed to travel for meeting clients and work at client location
2. How long may she stay in the destination EU member state
3. What is the 90/180 rule regarding the duration of stay?

My understanding of the 90/180 day rule regarding the 3rd question is that, one can travel from Germany to, say Warsaw, and stay there for 30 days in January. Then according to the rule, one can only travel back to Poland after 180 days after the first entry into Poland (sometime in July?). Or can one travel immediately, say in March?

Answer 1

As far as travel rules are concerned, she may stay in another Schengen country for 90 days in any 180-day period. How does the Schengen 90/180 rule work? provides more detail but if she has spent 30 days elsewhere than Germany in January, she still has 60 days to use (at once or split in several shorter periods) between February and April so there is nothing stopping there from taking another trip immediately. After April (technically 90 days after she left at the end of her January trip), she might even stay for a full 90-day period (and not merely for 60 days). This type of travel to other Schengen countries is allowed for any purpose, including business trips, and the time limits are not enforced strictly.

The tricky part is that working might require additional permission and going beyond typical business trips might trigger other rules (taxes, insurance…) that complicate the picture somewhat. So meeting clients, a longer stay to negotiate a contract or kick-off a project, even being out of the country about half of the time meeting different clients across Europe all seem OK to me but full-time on-site contract work for a couple of months at the same place might be dicier.