Italy was openly hostile to Austria-Hungary. No way she was going to fight for Austria-Hungary in an offensive war.
That said, even if she did. Ask yourself, if the weak and ineffective Hapsburg army could curb stomp the Italians for 3 years, what makes you think the French would have any sort of difficulty? Not to mention the barely functioning Italian economy would have collapsed within a few weeks due to British naval blockade. Italy would have been not but another corpse for Germany to be shackled too.
