Fantasy YA heroine's journal, use pseudonym to do magic

[Marta Magdalena]

This is a long shot as I don't remember much, but it's been haunting me for weeks.

It was a teen/YA book, written from first person POV. It was made to look like a journal/scrapbook, with handwritten notes and loose papers and little drawings. I think the cover was black and it was rather large. Now, I don't remember much of the plot but I think the heroine finds some magical journal or something? In any case, it was about magic and I remember very vividly that the main rule was you had to have a fake name to do magic with or otherwise the evil spirits/other magical beings could control you. The heroine also had a best friend A-type girl who was hell-bent on getting into an Ivy League college and constantly obsessing over her GPA. I also read this book in Polish, which means it had to be translated into a few languages. I think I read it around 2008 and it was pretty new then.

Sadly, that's all I remember! If anyone has an inkling what book could it be I would be very grateful!

[Kate]

Marta Magdalena ~~
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Good luck!

[Kris]

Marta, can you give examples of how the girl uses magic? Who teaches her?

What's the location (country/region/city/small town or a fantasy world)?

[Anna]

The fake name part sounds like Skulduggery Pleasant. It was definitely translated into Polish but I am not sure if the rest of the detalis fits or not.

[Stephanie]

Bump because I am genuinely curious as to what this book could be.

edit: actually, any chance this is Cathy's Book or its sequel?