The Two Letters
I speak some Spanish, so out of curiosity I paused my blu-ray to read the original letter from Fiamma's father. I noticed it had some differences from the English translation that we see Miss G. reading. The Spanish letter says that Fiamma had "un amor ilicito con un hombre mayor, un vecino" - an illicit affair with an older man who was a neighbour. I think if it had been a situation where Fiamma had an older boyfriend, the letter probably would have said "un chico mayor". The fact that it says "hombre" suggests that she was probably abused by a man in similar circumstances as she was by Miss G.
The letter goes on to say that the resulting scandal was so bad that Fiamma was forced to leave town. This would explain why she doesn't think she's being punished. She just thinks she's hiding until the heat dies down and then her dad will come and take her home. The letter says that she's being sent to the school to learn discipline and that her actions have consequences and so on. Again, Fiamma doesn't seem to think that her dad's angry with her or that he wouldn't want to speak to her when she called him. After all, she got that bitchin' parcel not too long after she arrived. My guess is that it's easy for him to blame her behind her back for what happened to her but he can't bring himself to do it to her face because it would mean having to confront his guilt over failing to protect her.
It would also explain her reaction to Miss G. following her into the changing hut after her asthma attack. It's not anger or irritation that this woman who nearly just killed her is still bothering her, it's fear. She's been down this road before. This is not a threat that a teenager, even one as worldly as Fiamma, would typically anticipate in 1934, or even in the modern day given that there are still so many people out there who honestly think it's impossible for a woman to be a sexual predator.
Whoever translated that letter into English must have felt sorry for Fiamma, because they changed it to sound more like a Romeo-and-Juliet scenario. It only says that it was "a neighbour" with no mention of his age. It says that they made "a failed attempt at an escape", something which the original letter doesn't mention at all. It also leaves out Fiamma's dad calling her "stupid" and "foolish".
So who is Pablo, then? My guess is that he really was just a friend, or possibly a boyfriend. Maybe his and Fiamma's relationship overlapped with whatever was going on with the hombre mayor. Maybe he tried to vouch for her somehow but nobody believed him because he was scruff. Thoughts?