Hey Marta,
This is a tough one.
I admire you wanting inclusivity, which is great.
But at the same time, you have to be careful not to step on French laws by suggesting that Muslim girls may wear scarfs in French schools.
For clarity: I have no relations one way or the other with any religion, except that I respect anyone and everybody who does.
Have you actually been asked by the girls, their parents or the school to cover their heads?
Point being that sometimes as director/producers we might take it too far to protect the people in the film, when their wishes may be not to be changed.
There are difficult questions to ask, but the answer(s) might create a solution that is easier to manage.
I take it that you have already got permission by the High School to film on premises?
If so, do the High School have public media release forms signed by parents for all of their students? (This is quite common for UK schools involving kids under the age of 18)
Are the girls in the background, or foreground?
Are they being interviewed, or speaking to camera, or just “extras on the set”?
If extras on the set, will the viewer identify their religion? Or is it a concern that being in shot might upset the family and their values?
If interview, find out if the girl wants to have a digital scarf wrapped around their head?
Or, although not desirable, maybe reshoot the interview outside the school, with the school in the background?
The above is the easiest way of getting around the problem.
But failing that, there are plenty of 3D depositories where you can buy everything that you need.
Blender is free to use, and there are compositing courses on how to use Blender for video. Otherwise, there are compositing software such as Black Magic Fusion where you can import 3D models into the video.
But there is every chance that when you watch it on the big screen, that you might regret the result – really depends on whether you can find someone who is really good, and can match “the grain (noise)” from the video onto the scarf to make it look real.
One depository that I found doing a quick search is this one:
https://www.cgtrader.com/3d-models/hijab
Hope that this helps?
Atb
Mads