There is no quote describing Blanche as a cat with a tin can tied to its tail, but there is a very similar quote where she compares herself to a kite with a can tied to it. The exact quote, from scene 9, is as follows:
Kiefaber, Stanley and Shaw have tied an old tin can to the tail of the kite.
At this late stage in the play, whatever remains of Blanche's world is rapidly falling apart. Her brother-in-law Stanley is driving her out of his house and her hopes of marrying Mitch have been shattered as he has just found out about her lies and hypocrisy. Kiefaber and Shaw are men who have told Mitch about Blanche's sexual promiscuity. Blanche tries to defend herself by claiming that they, together with Stanley, are just spreading nasty rumours about her. They have destroyed her last hope of happiness by turning Mitch against her. Blanche had hopes of soaring along with Mitch in love, but now the gossip about her has put paid to that. This is why she compares herself to a kite that is now being dragged down.
Mitch does refer to Blanche as a cat earlier in this scene, when he passes on Stanley's accusation that Blanche has been 'lapping up' liquor 'all summer like a wildcat.' Being compared to a wild animal shocks Blanche. This is the first time that Mitch has acted so coarsely towards her.
Thanks very much for correcting me. I had been looking for this quote for a long time.