I know that Lupa is supposed to stay at the Wolf House and only train them and all but in The Lost Hero she wasn't there during the Battle with Porphyrion. Also I'm really blown that she wasn't in the Son of Neptune. I think Rick Riordan might be getting our expectations up so that in one book she'll come and it'll be more exciting. It's definately a less anxious wait for The Mark of Athena then it was for the Son of Neptune because when waiting for the Son of Neptune we didn't know if Percy had his memory, if he'd get a new girl, who'd have their POV, Who from the Romans were a part of the 7, Camp Jupiters name and structure, Reyna's personality, etc.
So yeah, I kind went off topic but thoughts and opinions on Lupa.