The downside is that if she were to edit the PDF on the Windows computer, those edits will presumably be lost if she changed the document in GoodNotes, but if she is careful about that, I could see this approach working as well.) It seems that if you edit the note in GoodNotes the backup process automatically updates the PDF on the cloud storage, so this might been an option. (Edited to add: I did discover that GoodNotes has a feature where you can set up a backup location on a cloud service and have GoodNotes make those backups in PDF format, which makes them accessible on Windows.

Since the school provides a Microsoft OneDrive account (and access to the Office suite) she will have sufficient storage space for whatever is needed. In playing with it a bit, is seems quite usable possibly the biggest complaint may be that it provides a kind of unlimited canvas rather than logically creating pages of specified dimensions as one might do in Notability or GoodNotes, but she can presumably work around that. The only thing I have come up with that seems applicable is Microsoft OneNote. While Evernote is cross platform (and while I don’t love it, it is quite usable, she is familiar with it, and it does work), unless there has been a recent change, I do not believe Evernote supports handwriting / Apple Pencil. If the school was Mac-based, I would have had her try out Notability and GoodNotes and see which one she prefers, but that is not the case. Adding figures, pictures, PDFs, etc would be ideal. Typing into the notes will be convenient but not absolutely necessary. In additional to the cross platform requirement, she needs to be able to take notes in handwriting (Apple Pencil). The idea is for her to take notes in class and studying on the iPad, but have all documents available to her (in a convenient and usable manner) on the iPad and Windows laptop, and if she wishes also on her MBAir. Therefore I am looking for a good cross-platform solution for her. While she does have a MacBookAir (circa 2015), her computer for school will be Windows (the school issues the laptops to all students, so sadly this is not negotiable).

My daughter is planning to take class notes (medical school) using her iPad Pro and Apple Pencil 2. I was wondering if anyone might have some suggestions regarding a note taking app that is cross platform - Mac, iOS, and Windows.

Goodnotes to onenote