I don't know what state you're in or the laws there so I don't know if you are "obligated to talk to her" (I suspect not because if you wanted to, you could always get an attorney and force W/C to contact them instead of you) but there are reasons that a W/C rep would be calling you besides making your life more difficult.
W/C covers everything from time off work (time loss pay) to straight medical bills to voc rehab or compensation related to permanent disability/damage. One of the things they are responsible for is estimating this cost - for them and the employer. Getting your side of the story is a key factor in accurately estimating this. How quickly a person recovers and is back to full duty (or light duty) is also often directly related to how motivated they are to do so (ex. if in P/T they give you exercises to do at home, do you do them? Do you refrain from smoking if it is affecting the healing process? Do you exaggerate the pain you are in to extend the time off work?) Doctors (especially chiropractors) can also be motivated to slow the healing process or misrepresent how injured a person is because many see W/C as an eternal cash cow. (I say can be because I went to one chiropractor who repeatedly asked me if my injury was work-related and then told me I would have to see him for at least 6 months to resolve the issue. I could definitely see him being the guy who would tell W/C that I needed adjustments for the rest of my life. The one I saw most recently told me if I did the exercises he suggested and/or walked 3 miles every day, I shouldn't need to go back unless something acute happened. Guess what, he was right.)
My suggestion would be to not see the rep as your new best friend (of course) but be professional, answer briefly but accurately to the best of your knowledge and consider the calls with her to be a part of your job and return to work.
It sounds like you are motivated to get well, do your job well, and taking the healing process seriously. As long as you continue to communicate that to the doctor and at least semi-cooperate with W/C, your doctor should have a lot of control over how long you get the P/T. (Note: If this takes forever and/or you are really difficult to work with for W/C, you could be referred for an IME - Independent Medical Exam - which would mean you would be going to an unbiased third party to determine how you *really* are doing.)
