Editor's note: Inc.com columnist Alison Green answers questions about workplace and management issues-everything from how to deal with a micromanaging boss to how to talk to someone on your team about body odor.

A reader writes:

One of my coworkers is constantly telling me what to do, and it's driving me crazy! She does not give suggestions; she gives orders. She also disagrees with me on everything and insists on always having her way, both for things directly related to my work and things that are indirectly or not at all related to my work. Even the most insignificant thing will set her off. For example, we recently cleaned out some old filing cabinets, and my coworker demanded to know why I wanted to save a particular file since she wanted to throw out as much as possible. I explained why it was necessary to save these papers, and she disagreed and told me that I had to throw them out. While I understand why she wanted to clear out as many papers as possible (I did too!), her response to saving 10 pieces of paper was extreme, especially since we threw out thousands of other papers. If it were me, I wouldn't have given a second thought if someone wanted to save ten pieces of paper, much less made a big deal about it.

In addition to disagreeing with and giving orders to people, she constantly inserts herself into conversations she overhears that she is not part of in order to express her disagreement and tell people what they should do. For example, a client recently came to my office for an appointment with me, and said he would have to reschedule because he forgot to bring money for the parking meter. I asked him if he would like to move his car into our validated parking garage (which he did not know we had), and my coworker, who happened to be standing nearby but was not part of our conversation, came over and told my client that he should reschedule his appointment with me instead of moving his car!

My frustration is growing daily, and I imagine that it is for my other coworkers as well (she acts like this to everyone, including our boss). The funny thing about this is that while I am not her manager, I hold a higher position in the company than she does, and have been at this company twice as long as she has. You would think that she would realize that I am not a clueless idiot.

Do you have any suggestions for how to deal with this? My department is small, and we all work closely together for very long hours, so it's important that we have good working relationships with one another.

You're going to have to be more direct and more assertive with her.

She's getting away with this because no one is pushing back on her enough. I realize that people don't always feel comfortable doing that, but you really only have two options here: to be assertive with her or to continue to deal with it. So you have to decide which you're most willing to do.

Assuming that you choose the path of pushing back, that means that going forward, when she's telling you to do something that she has no business instructing you on, you should use statements like these:

* "No, I'm planning to do it differently."

* "I have this covered on my own."

* "Thank you, but I don't need help with this."

* "I have it covered. Why do you ask?" (Say this in a confused tone, as if you're genuinely confused and even concerned about why she needs to know. Because it's appropriate to be confused by it.)

With all of these, repeat as needed. It's fine to repeat one of these statements several times if you need to.

The exact wording will vary depending on the situation, of course, but your responses should all be in the spirit of what's above ... in other words, erecting a very clear boundary that you're not allowing her to cross. Note, too, that these statements refuse to engage with her in the way she wants. She thinks it's appropriate to expect you to explain to her why you're not doing things her way, but in fact you owe her no such explanation. So don't explain your actions, and don't try to convince her. Simply assert appropriate boundaries and stick to them.

If she resists, you'll need to get even more direct and call her out on her inappropriate behavior. That means that conversations should go like this:

Coworker: "Why are you saving this file?"

You: "Those are papers that I need. I have my area covered and don't need help, thank you."

Coworker: "But why can't you throw them away?"

You: "Again, I have my area covered and don't need help."

(Presumably, at this point, she'll stop, but if she doesn't....)

Coworker: "Those really need to be thrown away."

You: "Jane, is there something I'm missing about your interest here? I'm making decisions about my own files. I don't need input about what decisions to make. Please give me the space to get my own work done and focus on your own work."

You might feel rude about this, but keep in mind that she's the one being rude -- not you. By behaving inappropriately, she's forcing you to be more blunt than you'd need to with a normal person. She's the one setting up that dynamic, not you, so don't feel that you're being rude in pushing back; your responses will be the polite way of dealing with a boundary violator without letting her run roughshod over you.

Also, if you want to, you could consider have a big-picture conversation with her about the problem, especially since it recently impacted work you were doing with a client. You could sit down with her and say, "The other day, you suggested that my client reschedule his appointment with me rather than moving his car. In the future, please don't insert yourself into conversations that I'm having with clients. You don't know the full context, but more importantly, it's simply not your work -- it's mine. If I ever need help, I'll ask for it -- but until and unless I do, I need you to let me manage my own work."

You'll probably need to do this a few times, but she should pretty quickly get the idea that you have boundaries that she's not going to be allowed to cross, and you should see the behavior change. And even if it does continue, you can continue setting and enforcing boundaries anyway -- she can only force you to change what you're doing if you let her.

Want to submit a question of your own? Send it to alison@askamanager.org.