So there should be 3 paths atm but I think only 2 are available. There is;
Redemption
- Talk her down, accept her gift
- Talk her down, reject the gift
Corruption
- Accept her actions, accept her gift
Killing Mara obviously... well, kills Mara. All her future appearances will not happen, her talks with LW, her at the Senate, future content in whispering brook showing the aftermath, her showing up in town, and her life after the game are done. She's dead. The gift gives you a small change, but rejecting her gift... will have other effects that I won't be spoiling.