Have any nemeses at work?

Made a nemesis for the first ever time at work recently. Really zealous individual who constantly tries to undermine everything I do (I.E trying to get involved in my team's work despite not knowing anything about the ins and outs of what we do, making snap decisions on things that often take ages for me to clean up).

The worst thing happened today when she published a report criticising one of my projects with the aim of taking it over herself. Basically all of her reasoning was factually inaccurate (she'd actually made up a load of stats and figures). She's also logged into a personal account I use that has a generic company password (my fault) and taken loads of information off that too.

Not really sure how to approach the situation tbh, as I am pretty apathetic when it comes to colleagues.