Both films were shot in summer of 1988, and released within a few days-weeks of each other. I am not in a position to say which was physically shot first, although it is generally and widely accepted VALENTINA to be her first hc title.
With regards to the question raised by Tintoretto about two Moana titles:
ABISSI VENIALI
(1994)
int: Moana Pozzi
ALTA PRESSIONE
(1994)
int: Moana Pozzi
Unfortunately I do not recall what was my source for these two titles being included in her filmo. I have no other information on them. It is quite possible they are not original works at all, but re-edited and re-packaged jobs like many of the Moana Pozzi movies that continue to surface from time to time.