But with the ratings what they are, it could use a boost.
Indeed.
You're right, but they also portray her as someone who is not a typical Luthor. Someone who does not want to go down the same path, and is not evil. They have her do all you mention, and I agree that her actions could absolutely be evil--but I don't know if the WRITERS feel that way. Maybe that says something about the writers, who have been dropping the ball on this show for awhile now.
They may not feel that way, in their neverending, boring push to have everyone do the Marx Brothers walk down the street, but this series has never developed a great villain, or if there was strong potential (Lockwood), they are reduced to a cartoon character by the end of his run. Lena, being a "local", her corrupt, on-screen history and now knowing the truth (that her "friends" are habitual liars) cannot--with any sense of realism--just toss it all over the shoulder, nor can she make a moral pivot when her past actions are a part of her identity.
With good writing, I'm ok with turning her evil and the building blocks for that are in your examples. Instead of fighting, she could embrace her Luthor traits, and then let's see what happens.
...and being a human (who is not going to vanish after an arc like so many aliens on this show) and knowing SG's true identify would make her far more dangerous than any who came before. The one enemy SG cannot punch into submission. McGrath has the acting chops to pull that off, but I'm not betting that the showrunners will take Lena where she was meant be as an antagonist.