Credit the place of burial and what is (weakly) known about that, i.e., not a tar pit or source of construction materials but a place of burial for martyrs (inter alia?) purchased and prepared by wealthy Christians as an expression of piety; that there was a vial which appears to have contained her blood that was buried with her (give benefit of any doubt since that is very highly likely to indicate that whoever the girl may have been she was probably martyred) and we have a martyr of uncertain name (actual name is irrelevant compared to evidence of Christian martyrdom), some evidence that she was lanced and a claim that she was attached to an anchor and drowned (how hat correlates with the fractured skull is not immediately apparent.
The rest is pious stuff emanating from enthusiasts but based upon what may not very well be called evidence. Rather think of her as the unknown matrtyr because that is what she is. To presume an entire biography from what little evidence is available is the sort of thing that has often brought canonization into some disrepute.
If non-Catholics do not have confidence in our canonizations, I will survive. This sort of thing gives rise to a very reasonable skepticism among Catholics who care about the truth.
Pope Gregory XVI did not canonize a biography. He canonized an apparently martyred young girl. On one interpretation of the letters on the broken tiles above her grave, she was named (by Gregory XVI at least) at her canonization as Philomena. Fair enough.
Let us not be carried away by private revelations (if they were revelations at all) to assume biographical details entirely devoid of evidence. Many more people have been martyred for the Faith and whose biographies and even names are long and permanently forgotten on earth. We will know all of the truth when we are dead.
I will concede that even the meager available evidence seems quite persuasive that this girl was martyred, was martyred for the Faith, and thus a saint.