Contradiction with John 18:17
This verse states that the maid mentions Peter being a disciple of Jesus directly, whereas Mark 14:66 has a general account of the maid speaking about Peter.
John 18:17: Then saith the damsel that kept the door unto Peter, Art not thou also [one] of this man's disciples? He saith, I am not.
Contradiction with Matthew 26:69
In this verse, the maid mentioned is specifically identified as pointing out Peter, which could be interpreted with a slightly different nuance from Mark’s more general description.
Matthew 26:69: But he denied before [them] all, saying, I know not what thou sayest.
Contradiction with Luke 22:56
Here, it mentions a "certain maid" in a slightly varied context or sequence compared to Mark 14:66.
Luke 22:56: But a certain maid beheld him as he sat by the fire, and earnestly looked upon him, and said, This man was also with him.