In tradition, no one ever speaks of multiple ascensions of Our Lord. The Ascension occurs 40 days after this conversation with Mary. Most of the ancient commentaries on this verse consider that her attitude towards Him was not correct. She was happy to see Jesus again, wanted to be in the presence of that "man", wanted everything to be just like it was before and still saw Him as that Man rather than Who He really is, that He equal to God. Jesus could see this in her heart and admonishes her for that attitude. That was the traditional understanding of why He told her not to touch Him. There was never any distinction in time or sequence (of ascension or ascensions) between this appearance and all the others. They saw no need to suppose He appears here to her on His way to the Father then returns almost immediately to appear to others. He later clarifies His status as witnessed by His disciples and included in all the Gospel accounts. So in clarifying who He is (going to sit next to -right hand -ie same level-equal to the Father) it is a little bit of a kind admonition that she was not approaching Him in the correct manner.