So the consensus is that Mouse can’t counteract the Murphyonic field, but can alter the probability of failure, rendering it less likely over a given period of time, and probably cannot counteract a direct hex.
It does strike me that Mouses magic would work not only on the device but the practitioner. He helps smooth things out so that Maggie has a good day and doesn’t lose control, and it’s when Wizards are emotional then the Murphyonic effect is worse. For example a computer screen freezing would frustrate a wizard causing him to blow out the computer, and the frustration of that would have him taking out every device in the vicinity, in an escalation loop
Mouse would stop the screen freezing too long and/or prevent the wizard getting frustrated cutting the escalation loop. This could be useful if Maggie developers powers and goes to school, preventing her taking out all the IT in the classroom, he genuinely would be an emotional support dog....and an IT support dog. Well he was named after a piece of computer equipment. This would allow Maggie to have a more normal childhood, which would be Mouses aim.