low back pain and anxiety in 85yo female resident-HELP!

In our personal care/assisted living , I have an 85 yo ambulatory female with short term memory loss and acute anxiety. When she came around 4-5 months ago, she suffered from mild anxiety related to loss of home, new surroundings etc. She is aware of her forgetfulness, has a marvelous sense of humor, ie when she is given her meds , she says "Are these my birth control pills" -she was never married and states she had never dated more than casually! She's a hoot! The problem is that she fell about 6 weeks ago and now suffers from "grabbing" pain B/L low back. Darvocet, vioxx prn are prescribed. She has been receiving only Darvocet, which takes the edge off only. The problem- X-rays show no fracture, and the pain is exacerbating her anxiety. She stays in her room except for meals and repeatedly questions her prognosis and reports her pain. The MD prescribed Buspar. When I was showering her for an aid on Sat evening, she showed me bruises on her knee, and when I questioned them she stated that she has been biting them, I am the only one she trusted to tell, and she said "I'm so ashamed". Of course I reassured her that it was nothing to be ashamed of and that it was the right thing and the healthy thing to tell me, and I talked to her about positive and negative coping methods and tried to reinforce them over the weekend. Her attention span is very short, and reverts immediately to the anxiety mode. I feel that the other staff (by experience) will not continue these efforts and the woman will fall through the cracks- and the MDs will just medicate. What kind of injury can cause this kind of pain-would it be soft tissue? Spasms? And what can I do to help her? Please advise. Thanks very much in advance.