The new employee on my team turned out to be a snake and my manager isn't doing anything

About two months ago, we hired someone named Sarah (42F) for a middle-management position on my team. She doesn't have any direct reports yet. For context, I'm in a senior role and my manager is a C-level exec.

From day one, her level of brown-nosing was off the charts. Honestly, it grosses me out. Every idea I had was 'revolutionary' to her, and everything I did was 'genius.' It's so artificial and over the top. I tried to handle the situation and told her I wanted her to feel comfortable and that my goal was to help her settle in, but the brown-nosing continued.

Three weeks later, she started telling anyone she met that our manager is a 'visionary' and 'so inspiring.' I mean, seriously, you've spoken to him for a total of 5 minutes.

A few days after that, my manager told me that Sarah had come to him with some 'concerns.' Apparently, she feels isolated, thinks I'm not guiding her enough, and that some of my suggestions are 'a bit unconventional,' but she's afraid to object.

This drove me crazy. First, I personally handled her entire onboarding, we have regular 1-on-1s, and I make a point to check in with her every day. Second, I always involve the team in decisions, but she just agrees with everything I say. The other three people on my team have no problem speaking their minds because they know I appreciate genuine feedback and different perspectives.

Look, my manager and I have a good relationship, so this isn't going to get me in trouble. But he's extremely non-confrontational and doesn't understand what a big deal this is. I was obviously furious, but he told me to just let it go and maybe double-check that she feels supported.

So this morning, I sent her a message asking if there was anything specific I could do to help make her job easier. She replied that everything was fine and sent a thumbs-up emoji. I replied, reminding her that my door is always open, and then I took a screenshot of the conversation.

So now I'm stuck with this snake on my team, and there's nothing I can do unless she tries something bigger or really screws things up. It seems I'll have to watch my back from now on.