At my school it was my form tutor who wrote mine aswel, but he took into consideration what all my subject tutors had to say. However, me and him wernt on the best of terms (he hated my guts lol), so he wrote me an absolutly dreadful reference (and I mean really, really negative things such as "immature", "over-confident", "took a while to settle in at college" etc etc.)However, it doesnt really seem to have worked against me.
I highly doubt your tutor would write anything negative on your reference; if she hardly knows you then I would think she would just write the usual stuff about how wonderful you are etc etc. I personally dont think admissions tutors put THAT much emphasis on references because they are all the same. Those applying for top Law schools will all pretty much have perfect references, and admissions tutors know that forum tutors tend to just write pretty much the same reference for all students and just change the name in it. I would say that out of all the things taken into consideration (GCSEs, AS, A2 predictions, personal statement, LNAT etc) the reference is the least important. I sometimes wonder whether admissions tutors even waste thier time reading it. I mean just looking at my reference it makes me laugh to think that Nottingham and KCL read this and still offered me a place.