This is a very good theme to focus on, but if I may make a suggestion, you might like to think about how you can expand this theme to not only focus on the monster but also on Victor Frankenstein himself. Both characters are isolated, although it is the monster alone that faces rejection.
Note how the monster's isolation is something that is not chosen, but imposed on him by a humanity that has rejected him and his own creator who has abandoned him. His longing for fellowship with others is evident, and this longing is made all the more terrible by the love and affection that he sees in those around him and the awareness that, because of his appearance, he will never be able to share in that human warmth. Note how he comments in Chapter Twelve when he observes his "friends" as he calls them:
What chiefly struck me was the gentle manners of these people and I longed to join them, but dared not. I remembered too well the treatment I had suffered the night before from the barbarous villagers...
He is a creature who is shaped so much by his experience of rejection and isolation, and Shelley actually suggests that what has driven him to become inhuman is actually the inhumanity of man. Note how he says "I am malicious because I am miserable" to his maker. We are left thinking that the "monster" might not have been quite such a "monster" if his maker had actually cared for him and looked after him.
Victor insists that his isolation is a result of the monster's terrible crimes which dictate that he must be an outcast. However, he chooses to isolate himself willingly to carry out his experiments, making us doubt this reasoning.