Morgana turned Gwen evil witb her ways...

I think that Morgana has somehow brainwashed Gwen kwa taking her to the Dark Tower, whereas i think that it was zaidi of a natural occurance with Morgause and Morgana is her sister so they would have a strong bond.

No. Morgana wanted to kill Uther kwa S02. When Morgause asked Morgana if she actually wanted that to happen, to become an ally, and would do what was needed, Morgana willingly alisema "yes". So, Morgana willfully agreed to kill the king and undermine the kingdom.

Gwen on the other hand was exposed to the mandrake root which allowed Morgana to gain control of Gwen's mind. After Gwen was brainwashed kwa Morgana, she exerted her control over Gwen to commit "evil acts." Had Morgana not used the mandrake, it's not very likely that Gwen would willingly try to kill Arthur au undermine Camelot.

I don't think she's done anything 'magical' as such to Gwen. I believe that Morgana over-exaggerated about the bad things that Arthur may have done to her. And because of the horror Morgana put Gwen herself through, she thinks that is how Morgana felt.

I think morgana did brainwash gwen and then forced her to always wear black when she sees her