I'm sorry but she doesn't necessarily need to actually have his favor it's far enough only to be a sister or acquaintance enough for him not to execute her all she has to do is stay away from the ML and FL and any setting of the story.
If I was reincarnated as a villainess the first thing is to establish relationships and ignore The FL and ML, also if there are extra leads. It is to never fall inlove with any of the leads because doing that would somehow lead to getting entangled in the plot of everything.
Second is to try and cut ties with those who have any major things in the plot but not like completley because I need favor in order not to die. I will have to stay as far away even if that means moving across the country and THIRD the most important that leads back to falling inlove with the leads is to never show favor or get attached to anyone there that's specific to plot and forth is to not intervene with anything meaning no "OOPS THE ML FELL FOR ME WHEN I WAS HELPING HIM GET WITH THE FL"
All of these are those most necessities of being NOT-A-VILLIANESS.
If it helps and you do find yourself in a situation like this make sure to thank me
Also if it helps try finding all the male leads weaknesses and gather as much same gender allies specifically mostly the same gender because they are most likely to help you or strong people who favored you from the beginning and even if it means to manipulate innocents do it because remember you could have a happy ending with those you manipulate if you wanted but just know everything is fiction they are all mindless zombies doting or hating on the FL. So just do it for your life in order to live happily then if you managed to come/live this far in order to do so you must also make sure to write the info down and write all your relationships, and if you're on their bad side or good side or just neither for more practical protection purposes also try learning fencing or maybe archery to save you in the oh no the ML is about to kill me situation.
This might be random but ifyky