Midline Discrepancy? What are my options? Do more IPR?

Hello, I had removed upper/right 2nd premolar for braces. After 18 months my teeth are straight but my midline is shifted to the right, about 3 or 4 mm (to the mid of my face). My ortho said ther was no space to moved it to the left. She did some IPR but I don't think it is enough. What are my options? Do more IPR? How much space can I get that way (do you think 3 mm is possible?). Elastics or TADs? I don't want to extract tooth! P.S. my lower midline is ok with face.