In doing so she discriminates against Alan, while keeping from him the discrimination involved.
In doing so she discriminates against Alan, while keeping from him the involved discrimination.
Which of the above sentences are more idiomatic?
In doing so she discriminates against Alan, while keeping from him the discrimination involved.
In doing so she discriminates against Alan, while keeping from him the involved discrimination.
Neither of these clearly convey your intended meaning.
Instead, say:
"In doing so, she discriminates against Alan and hides it from him.
or
"This way, she discriminates against Alan without his knowledge."
or
"In doing so, she secretly discriminates against Alan."
The last example can also mean she is concealing her discrimination from everyone, and not just from Alan.
Since involved can mean "complicated" when used adjectivally, it's a shade better to write
In doing so she discriminates against Alan, while keeping from him the discrimination involved.
if your meaning is "the discrimination that involves Alan".