There is no need to cancel the existing I-130. They allow having multiple active I-130/I-140, and the immigrant can choose to complete the process through whichever one progresses to completion first.
Go ahead and file for your mom with a new I-130.
PD: Jan 2003 (EB3 rest of world)
I-485 Approved: July 2007
I am a layman, not a lawyer. What I write here is not official or professional legal advice. In addition, my answers on this forum are specific to the scenarios discussed in each thread and should not be generalized to other situations.