Letter of recommendation from TA?

[pws]

I just finished a Poetry in America course at Harvard Extension, and I'd like to ask for a letter of recommendation to apply for graduate studies. However, the course professor basically has zero contact with students, and doesn't read any of the written assignments either—which is all done by a teacher's assistant (TA). Although the TA is a college professor herself (at another school), I don't know how having a letter of recommendation from a TA, as one of the two needed references I need for the graduate application, would work out.

Has anyone had experience with a situation similar to this?