Sasa is kind of really stupid and as long as she doesn't catch you by surprise, her "mind control" doesn't even work that well.
She may have pet witches, but that isn't really a problem for us.
Unless she gets a major power-up or grows a brain she isn't much of a threat.
On the other hand, memory rewrites and her possibly deciding to go after, say, Mami or Madoka to get to us...or even just throwing a monkey wrench into plans are definitely worth being concerned over.
Personally, I think we may need to scare her- murder's off the table, but she's a fairly awful human being with no excuse for it and bad behavior patterns.
Some ideas:
Plan A: Threaten her into knocking off her little attempts at territory grabs and/or Witch pokemon and send her on her way. She won't like being intimidated by someone 'better' than her, which will cause problems, but it might keep her from pulling shenanigans. Also, sending a petty, small-minded mind controller with a thing for grudges away with a chip on her shoulder.
Plan B: Be nice. No, seriously. Run into her, trounce her, give her a rant with the promise of Consequences if she abuses her power like that, maybe try and get her to...well, stop being terrible, and after that treat her as any other stray magical girl in need of cleanses.
Plan C: Gem her if she does something offensive, grief-rend the body, and deal with her later. My least favorite plan and probably going to be an emergency contingency for if she does something stupid around Madoka, but still better than her getting murderfaced, if only for the sake of Homu not being a murderer where word might spread to our other friends.
EDIT: Goddamnit. Guess I know what we're going to do when we return to Mami...