I keep wondering if her amnesia and past are realistic and somewhat mundane, or a bit out there but still grounded (like being a "cleaner" for criminal work), or even fantastical like being immortal.
nah, I think it will be some fairly normal tragedy / trauma.
I assume she lost her family in an accident which also caused her memory loss.
at one point she will remember that and feel incredibly alone, after all her complete family is dead. but then all her friends show up and lift her up again, showing her that she is not alone.
thats my (fairly baseless, because the author gave only very little hints til now) assumption at least.