I'm thinking about approaching a petty co-worker

I don't have a lot of confirmed examples but I'm pretty sure I have essentially a "tattle-tale" co-worker. After I returned from maternity leave myself and the team suddenly started getting hounded for being even a few minutes late (which obviously is difficult when you're not getting sleep and trying to establish a routine and get a kid to daycare for the first time). It dawned on me that our leader was mostly not in his office when we got in so I'm pretty sure our admin was basically telling on us to shed a bad light on us, maybe particularly me. It was strange because I had even had conversations with my boss before this that my schedule was flexible and I didn't have to have a strict 9-5 schedule, just not to be late to important meetings. This strictness came suddenly and then later it got quiet when the admin was moved to a different department, although, occasionally she would come down and "check in on us" when there was just a couple of us younger workers in the office. It's wild to me because although I'm pretty junior on the team, I perform well above my job description and have more direct contact with big decision makers than most of the team. I've also seen this person actively "campaign" against other employees she doesn't like and I think she manipulates my boss's opinion on them. I've heard her describe interactions with certain people that I witnessed and she really embellishes to make them look bad. So much once that I actually had to go to my boss on the side and let him know that that wasn't how it happened because I was afraid he would take action. This morning I had a meeting with her and her new boss at 930 and I was rushing to make some last-minute, time-sensitive schedule changes for an interviewee coming in so I left my desk at 931 to go about 20 feet to our meeting and MY boss hears me say goodbye and goes "oh good, *petty coworker* just texted me asking if you were coming." Besides the fact that her boss wasn't even there yet either.. she didn't message me. Not a word to me.. she texted my boss at 931 to makes sure he knew I was not there yet. I'm so over it. I've mentioned the campaigning to a manager on our team before so I thought about telling them about this but now I wonder if that means I'm just tattle-taling too. I'm considering having a conversation with her but I'm not exactly sure how to go about it. I'm not really afraid of the confrontation but I am worried it could put an even bigger target on my back and she may then go embellish to others the way I approached her. I think her and my boss have a closer personal relationship than they put on because he seems to protect her or at least have blinders on when it comes to her problematic behavior (including poor performance). Anyone go through something similar? What were the results?