Sounds like you have a good reason to feel that way. Did you ever talk to her about your problems in class? Some people are amazingly unaware of what they are doing to others and need a wake-up call.

Do you know this woman outside of school? If not, then you don't owe her anything, in my opinion. I certainly wouldn't write a letter of recommendation for someone who can't contribute to the work load.

If you work with her, or socialize with her out of school, then it could get awkward. If you feel you must write a letter for her, make it very bland and simple - I've done that a few times. Just state the facts: Tell who you are, how you know her, and add a line that they can contact you if they have questions.

Most employers have learned to read between the lines of these letters and they'll get your drift.

Good luck!