Is it my responsibility?

I am not a trainer or manager. I have slight seniority, yet our org has a flat structure with only one leader and many direct reports. I share an office with a new coworker. She just finished her onboarding window but is still drowning and not quite catching on. There are several things she does right, but the amount of time it takes for her to get going or start a task is not sustainable or requires me to stop what I'm doing to show her. I have chatted with a few coworkers about it previously against my better judgement yet out of frustration. One seems to have a bit of a personal disdain for her, while the other questioned her competency from day one. They both feel that I should go to my boss, and reiterate she's not cutting but there is no way that our boss isn't privy to XXXXXXXX not working out. We have weekly one on one's to discuss projects, various team meetings, and such and I know there have been balls dropped. I do not feel that it is my place. I do share with my boss in my meetings that I'm frequently interrupted or where she is needing assistance, but I also give her praise where praise is due. My boss apparently shared that information with the team member that deems XXXXXXXXX is incompetent and feels that I'm doing us a disservice and need to be harsher because my boss implied that I'm painting XXXXXXXX in a positive light. I firmly believe that my boss does not share everything with either of us, and feels that it would be inappropriate to discuss anything that was critical of another team member and reiterated this to my coworker. I've been in leadership, and am one of the few on my team that has any prior management experience, which is why I feel that I'm doing what I'm "supposed" to do. However, I know times have changed and have a nagging feeling that perhaps I am dropping the ball.