How do I deal with a passive-aggressive, subtly bullying colleague?

I’ve worked at a small organization for about 8 months now and have really assimilated well to my new position. I’m youngish (25) and still learning the ropes of a new industry but I’m happy, productive, eager to learn, and very cordial to my coworkers—with whom I mostly get along well enough.

One of my coworkers is a woman in her 60s who is very good at her job, and outwardly appears very friendly and likable. When I first met her, I thought she seemed great but I quickly realized that she’s one of those people who can insult you with a smile on her face, leaving me hurt, confused and frustrated.

For example, while she smiles at me and seems to be kind, she’s actually very condescending and talks down to me like I don’t know how to do my job. Keep in mind, that this woman is senior to me but she’s not my boss or my supervisor. She’s even gone as far to describe my job description to me like I don’t know what I’m doing and need her to hold my hand.

Whenever I have to work on a project or assist her with something, I dread it and actually feel anxious. Number one, she’s a notorious bottleneck —she’s never satisfied with anything I do and I’m starting to think that it has more to do with the fact that she doesn’t like me and is trying to set me up for failure or sabotage my career. Simple tasks take forever to work through with her because good enough is never enough.

She’ll come to me with a seemingly simple request but then complicate it with confusing and contradictory directions, leaving me stressed and bewildered. Then, she acts like I’m an idiot if it’s not exactly what she wanted on the first attempt and take the opportunity to demean me and make me feel like an idiot for not “comprehending what she wants.”

Tonight, I actually left work crying. She held me hostage until 7:30 pm with another one of her harebrained marketing requests. This one seemed simple enough—copy for a promotional flyer for a conference she’s attending.

Except, as always, she starts rambling on with her excessively complex directives. I grab something to take notes with and she asks “Um, are any of my directions going to make it to the final product? Because that’s something you struggle with. Just some feedback for you!” Like it was the most natural thing in the world to insult me and went on to take further little stabs at me as well.

I’m so sick of this behavior and I’m at a loss for how to deal with it. Naturally, I’m shy and not good at confronting people directly. I stutter and I’m afraid I’ll even burst into tears. :( I almost want to say something to my boss who I have a good relationship with but I’m not sure how to approach this because this woman has been with the company for years and has plausible deniability.

Help!