My Latias´s moves are:
Dragon Pulse: STAB
Recover: To gain lost health
Heal Pulse: I´m more of a double battle person
But I don´t know any good item for her.
P.S: Nature: Jolly.
The Soul Dew is considered the best item for Latias
The Soul Dew is a Latias/Latios-exclusive item that raises both their Sp Atk and Sp Def
If you can't get a Soul Dew then here are some other items
Petaya Berry - Raises Sp Atk when HP falls to 25%
Lum Berry - Deals with any status ailment