Let's look at this logically. The facts are: she is hinting that she likes you, but hasn't come right out and said so; you don't like her in return, at least not in 'that way'; you would prefer to keep the friendship, in part because she offers a convenience which you've come to rely upon; you already have a girlfriend, and she knows this.

What are your options? First, you can continue to play dumb until she forces the issue. This probably won't work, since you're already uncomfortable with where things are now, and she still (unfairly) thinks she has a chance.

Second, you can simply cut her off, and find (or buy) another printer. While this may seem the easy way out, there's a risk that she'll continue to pursue you; and even if she doesn't, she's bound to harbor resentment and negative feelings toward you.

Third, you can choose to have a frank discussion and try to settle the issue. This is probably your best option, but it carries its own risks. If you decide to do this, here's my advice:

DO ask her first if you're reading the signals correctly. There's nothing more embarrassing than an unwarranted assumption on your part.

DON'T use the standard "It's not you, it's me" line. She'll know it's BS. Instead, remind her that you already have a girlfriend, you're happy, and that you're not interested in a romantic relationship. It may help to point out that you see her more as a sister and a good friend.

DO use plenty of "I" statements, including "I didn't realize how much you felt that way," and "I'm sorry if you felt I led you on." Telling her how you see and feel things is less threatening and accusatory than using "you" statements like, "You should've known I wasn't interested in you like that."

DON'T try to weasel out of hurting her by making an open-ended commitment you can't keep, like "Maybe someday." That just brings you back to square one; and when you have to go through this again later, it'll probably cost you the friendship.

DO be prepared that she's already decided it's all or nothing, and that you may have to just walk away. Nothing in life is without risk, especially when they involve matters of the heart.

DO let her know that you value her as a friend. Continue to do friend things like watching TV, having talks, sharing jokes, and playing video games together. If she feels that you're only trying to settle this because of perks like her printer, she's likely to be offended (and rightly so) and insist you move along.

If at all possible, DO try to include your girlfriend in your activities together. Part of her attachment to you may be that she sees your girlfriend as an abstract obstacle, rather than as a person. If you all spend time together, they may become friends as well; at the very least, she'll realize that you're already committed. (Just don't be all lovey-dovey in front of her; that's like rubbing salt into her eyes.)

And as weird as it may sound, DO look around, and ask your friends, for a guy who may be right for her. Sometimes what's coal to one man may be a diamond to another.

Whichever way you decide to go with this, the best of luck to you.

This. Ohhh yes, very much this.