I have never had mtDNA done. This is all based on yDNA male line from my brother.
The Butler lines all match back to William Butler b. 1775.
There are 6 distant cousins tested from his sons.
We match:
Ros Benjamin Lamb
John Craig Lamb
Roger Francis Sinnard (now deceased)
George David Thompson
I am not sure mtDNA would show any of the Lamb line. It would be your Mother's mother's mother's mother.