How to respond to potential power abuse from project supervisor? Over the space of a now concluding 20 week long project, my appointed supervisor has made a number of questionable decisions that appear to have negatively affected my work and solidified her grip over any avenues of complaint i can make.

One of the more recent incidents included her refusal to complete a strictly compulsory progress report, unless i removed a statement about her absence for a three week period that affected my ability to receive feedback. Stating during the incident, that if anything reported made her look bad, then it would be reflected on my final grade(As she is one of two, who marks the project).

Her general lack of support throughout the entire process has been difficult and while i appreciate that some supervisors and some students prefer the more independent approach, it doesn't work for me and I've made this clear many times. She has also enforced a number of design decisions that convert the project to a very similar format to one she had previously partook in. Additionally insisting on heavy reference to her previous work.

I'm at a loss of how to proceed and the advent of the global pandemic has only narrowed my ability to discretely contact any support staff.

UK, final year undergraduate student
Let me make two suggestions, though I can only really recommend the first. 

You could just go along and get along, but mostly as a strategic move that helps you get away without damage to your future. For a single course a nice grade would be good and you will have learned a lot from the project no matter what the write-up looks like. If it is to be published, especially as a joint publication, then you need to take care that what you say is actually valid, of course. I recommend this course since the professor has power over you and has threatened to use it against you. Strategic retreat is often the best course of action. 

The second, burn the bridges strategy, is to send the entire correspondence stream to the department head and ask for advice. This may be what you really want to do, and it might have some positive outcome for others in the future, but it is also the one most likely to damage you and your career. If you embark on this course, copy the head on all correspondence. 

There are options in between but most of them might have the flavor of one or the other of these. I recommend something closer to the first option. 

For doctoral research, however, the situation is a lot more dire and might require drastic (escape) action such as changing supervisors or even institutions. But your undergraduate program will ultimately be judged on a lot of things, not just this project.