AITA for reporting my coworker’s side hustle to our boss after she threw me under the bus?

I (25M) work at a mid-sized marketing firm, and I’ve been there for about two years. My coworker, Sarah (27F), started around the same time, and we hit it off early on. We’d grab coffee, vent about work, and even hung out a couple times outside the office. I thought we were friends, or at least friendly.

Here’s the issue: Sarah has a side hustle designing logos and branding for small businesses. It’s not a secret, she posts about it on her Instagram, and I know she’s made decent money from it. Our company has a strict policy against doing freelance work that competes with our services, which graphic design definitely does. I never said anything because it wasn’t my business, and honestly, I didn’t care. Live and let live, you know?

A few weeks ago, we were both up for a big promotion to lead a new client project. It’s a huge deal, more pay, more responsibility, and a chance to prove ourselves. I worked my butt off preparing, but Sarah got the spot. I was bummed but figured she earned it.Then I found out why: during a team meeting, she took credit for a campaign idea I’d pitched to her privately and implied I’d been slacking on my work. Our boss ate it up, and I got a talking-to about “stepping up.” I was pissed but didn’t have proof to call her out, so I let it slide.

Then last week, I overheard Sarah on a call in the break room, bragging about landing a big freelance client, one of our company’s direct competitors. She was using our office resources (like her work laptop) to do it, which is a major violation. I was already mad about the promotion, and this felt like the last straw. I anonymously tipped off our boss with a screenshot of her Instagram post advertising her freelance services, mentioning the competitor client. I didn’t name myself, but I’m pretty sure Sarah knows it was me.

Yesterday, Sarah got called into HR, and she’s now on a performance improvement plan. She might even get fired if they dig deeper. She texted me, furious, saying I “ruined her career” and that I’m a backstabber for not talking to her first. My friends are split—some say she had it coming for screwing me over, but others think I went too far by snitching instead of confronting her directly. My boss hasn’t said anything, but I’m paranoid this could blow back on me if Sarah outs me as the tipster.I feel justified because she played dirty first, but I also wonder if I let my anger get the best of me.

AITA for reporting her side hustle? Should I have just called her out instead?