I filled my taxes with my wife but I forgot to add her W2 and my federal was accepted already. Can I still add hers ?

[Bsch4477]

If the return has been accepted you can amend it. But wait until the return has been processed and any refund or tax liability settled before amending. 

[Mike9241]

it's highly likely that when your joint return is fully processed, the iRS will catch the omission and either adjust accordingly or send you a notice to approve of including her W-2.