What would you want a coworker to do with you if the tables were turned? Probably pull you aside and talk with you before going to the boss, right?

My suggestion would be for you to invite her to talk with you to do a “debrief” of the meeting. Ask her what worked, what didn’t, and what would she do differently the next time. The purpose of this is to give you coworker an opportunity to self-assess before you add your feedback. It will also tell you how self-aware she is and if she is learning from her mistakes.

After she has shared her perspective, give yours. Begin with what you thought went well along with the areas that could be improved. Share a story of a past mistake that you made and how you grew from overcoming it. Ask her if there is anything you can do to help her in the future.

At this point, you’ve reached out and offered her help. If she declines it or if her behavior doesn’t improve with clients, then, and only then, would you want to confer with your boss. I’m guessing that the client would raise a concern directly with your boss as well and your coworker would be identified at that point in time. Then it would be out of your hands and where it needs to be, between your coworker and your boss.

The bottom line here is, try to help her first. If it does work out, then you’ve done a great thing. If it doesn’t work out, then at least you made the attempt, and that was the respectful thing to do.