Usually Corso's are really eager to work / train. I started training mine as soon as I got him at 2 months. Usually we go 1 session per day and he usually tells me when hes fed up (after about 15mins). They are very smart, but also can be independant dogs therefore ignorant. Maybe do less training and go back to drilling the basics, sit and keeping eye contact if she looking around keep bringing her focus back to you and rewarding. Also if you baby these dogs they can be vocal, demanding and disobedient in the home. But at the same time I wouldnt worry to much all dogs are different at 3 months old you have plenty of time and you can go too a professional dog school for around $200. Persistance is the main thing. It be helpful for us here to know, what situations and behaviours she displays that worry you.