ArtisticFan - hope just getting a chance to get this off your chest in a safer environment has been helpful for you. Sometimes that is more needed than actual suggestions, imho.
Nonetheless, I do have one of my own. Since you say you mostly interview by email, what would happen if you were to include something to the effect that you are copying her on your email to them and that you will be sharing their answers with her for possible use in her quarterly publication, but that she might still need to contact them with additional or follow-up questions of her own for her specific needs. Perhaps also add in that since your deadline is so short in comparison you hope they won't mind if this initial email deals only with the questions for your specific needs at this time. If necessary for the understanding of the interviewee give clear information about where your report will be published and it's purpose and the same for hers. If you do that I think it might be a good idea to let the boss know your plan and make sure she agrees with how you describe the two products. Perhaps for repeat interviewees even include an acknowledgment that you realize they may have been confused or unnecessarily stressed by what might have seemed like duplicate requests and that you want to remedy that. Just make sure that somewhere there is a specific nod to the importance and benefit of her publication that differs from your work.
To my mind this may accomplish a couple of things. It may prepare them for additional contact without making your department look inefficient or conflicted. It gives her a built in reason for contacting them separately and makes it harder for her to make you look incompetent. It might make it harder for her to duplicate your questions without looking stupid herself as she obviously already had the information you passed on to her. It will give all the stakeholders a buy in.
If this has no impact, I would suggest another discussion with the two of you and your boss wherein the issue will be how to reduce confusion and complaints of interviewees. Suggest any changes to how you are sending this email and have the boss suggest that she be copied on them for a time to be better able to monitor how they are working. If you have in mind one or two frequent interviewees who are getting frustrated perhaps a joint meeting with them as well - they are stakeholders in this process, give them a chance to be part of the solution. Maybe mention ways you already reduce duplication, like the picture sharing or something better if you can think of it. Though this may seem to be giving her praise for laziness, it also is also points out the benefits of co-operating on the cross-over parts of your jobs. It might make her feel more co-operative in general and will certainly make you look big in the eyes of your boss as you can find a way to make her look good, though by now the boss must be clued into your frustration at the continuing difficulties. Making everyone feel some empowerment along with some responsibility can't hurt this situation any, imho.
That said, sometimes there are no solutions with certain people. I had the misfortune of dealing for 15 years with a very difficult co-worker who was actually in a higher rated position, though thankfully was not someone to whom I reported. Not having dealt with such an aggressive person before I was at first quite afraid of her and how she affected my work and my bosses perception of my work. It took a while to understand that our ever-revolving managers would quickly come to know her tactics, though none had the guts to do anything about it, and therefore anything she did to try to make others look incompetent was mostly taken with a grain of salt or ignored completely.
Being a highly knowledgeable subject-matter expert she really had no need to feel so insecure, as the managers proved over and over by not even attempting to address her behaviour. Eventually I just became amused by her futile efforts. I remember that in one meeting where she tried to make me look foolish, drawing gasps from some newer team members, I actually burst out laughing at her ridiculous tactic. I really don't understand someone like her. This was one of only two times where she suddenly backed off and gave me and my work some respect for a while. The other was when I blew up at her for a totally non-work related incident where she thoughtlessly did something that almost broke my very new and very very expensive glasses. Even knowing this is the kind of response that could bring respect from her, it is just not normally my way and I would not lower myself to her level by using counter-attack as a means of getting the upper hand. Whatever you do, don't let her change you as that would stay with you forever. (She wins.)
Now that I have been away from her poison for a few years, I actually mostly just feel sorry for her. Her job seems to have been her whole life and identity, (not surprisingly she had very few friends over the years and most just didn't last very long), and now she is near retirement but has nothing to replace her work. (I win but I am sorry she can't just enjoy her life the way I enjoy mine.)
It can be so true that you reap what you sow. To add even more cliches into the mix - This too shall pass, What doesn't kill us makes us stronger, and He who has the last laugh.... Good luck, though from your thoughtful posts I think you will do just fine.