Have any tips for establishing a pattern of behavior without arguing the details?

I run a small web design/development company and often work with other contracted folks either that I find or the client provides. There is a young designer (let’s call her Jill) I’ve worked with on several projects lately. Jill’s great at her job, intelligent, organized and we work well together so we’ve each provided the other with work in the last year or so. Unfortunately Jill’s professionalism in dealing directly with clients has a few holes.

I’m not her boss, but she’s always been open to suggestions, especially with the “business” side of things. So I’ve tried to illustrate how it could be damaging and how those situations could be handled better.

The conversations get sidetracked into arguing the details of whether or not her actions were called for in a particular situation. The single situations aren’t important, establishing the pattern is. I’d like her to see that any one of the situations won’t be a problem, but 3–4 with the same client will have that client looking elsewhere or at a minimum being more critical of our work as a whole. 20 minutes into the conversation she feels she’s justified everything and I feel I’ve failed to make my point.

Some examples of the behavior I’m talking about would be
– taking phone calls at the table during client meetings
– firing off snarky emails to client’s change requests
– bringing up client mistakes when it’s not productive
– very protective of her work

How can I establish the pattern of behavior without getting bogged down in the individual occurrences? At this point it’s not just about helping Jill (who may need a concrete experience with the consequences before she sees the problem) but also about improving my skills with managing/helping people which will come in handy in the future.

Thanks for the time.