What is the ruling on visiting a father who is separated from the mother, when the mother expresses her annoyance at his visit and speaking with him, considering it disobedience to her?

Obeying and honoring one's mother are obligatory, but she does not have the right to prevent her children from maintaining ties with their father and honoring him, because there is no obedience to a creature in disobedience to the Creator. This should be explained gently to the mother.