I tend to agree with you. Even if there was bad blood between DV and JDT, DV is still her granddaughter's mom. I think JDT has had no experience with the media or LE (in a professional context) where she understands what seems "appropriate" to say or not. I'm sure LE has told her not to share anything with the public like they do in most cases, and she's just not sure what to say. They also may not be sharing any information with her since she's not DV's next of kin or relative. She may know no more than we do, but she still wants to try to answer when people ask her questions. She seems to have said the same thing over and over IMO with the exception of a few things she said early in the case that may have been proven incorrect. I don't really get the bad feeling about her some people do.
Most of what JDT knows has been info she's acquired the same way all of us have - sleuthing. LE has told her nothing. She has received a little bit of info from one of the people that was with DV the night she went missing, but the story changes each time this person has talked to her and it's been conflicting info. So she's back to figuring things out via sleuthing.