I've been working on my current research project for nearly two years and I love the work I am doing and the fairly large team of people I work with.
I have one colleague who really likes new problems and challenges. It's a great quality in general, but she keeps working on my parts of the project. I think she just likes the change of pace and the new challenge since she's been working on her parts for so long, so I'm trying not to be upset with her, but I wish we would stick to the partitions we agreed to. It's not like she's finished her portions, we both have a lot still to do and I've been focusing on one of my sections, trying to wrap it up before moving on to the next. I've started to realize that she's doing my other section and is trying to keep it a secret from me. She'll ask me for pieces of data, code, or background information I have without giving me an explanation. She's done this to a lesser extant a few times in the past and I've always just chalked it up to her curiosity. In general I have a lot to do on the project and if she does a little work here or there on something that falls in one of my sections, that generally fine, but this time it's not just a small piece, it's one of my two deliverables for the project, half of my total contribution. It feels like I'm being scooped on my own project and it's hurtful.
I'm not sure how to proceed. Should I ask her about it directly? Should I work on that section like I have no idea she's doing it? Should I speak to our advisor? This project means a lot to me and I'm not sure she if she's just bored and wants to try out her hand on new challenges, if she thinks she'll do these sections better than I could or if she thinks this will help her authorship when we publish.
I *really* want our team to be collaborative and supportive (as it has been in the past), so I'm looking for a solution that won't damage team dynamics (i.e. I don't want to make her look bad, but I also don't want to give up this part of the project).