If she was writing that her Portuguese tax number is not being accepted by the Upwork system, then I am having the same problem.
I can verify my tax number on international tax websites, but for some reason Upwork is not accepting it. I tried putting "PT" in front of the 9 digits and also without it.
That site (vies), says my "VAT" number is invalid, but it's valid in Portugal! So maybe one of two things: (a) The tax number that Portugal issues is not compatible with the rest of the EU or (b) I need to be a proper company and not just be an individual which doesn't make sense at all! So if I can't provide a valid "VAT" number, I will be charged VAT... I will be charged VAT just for having an account on upwork with no work yet? That doesn't make sense!