Wikisimpsons - The Simpsons Wiki
Bart is apparently on rather good terms with her, chatting with her when he gets sent to Principal Skinner's office, and even giving her the occasional rose. He also knows about her relationship with Frank and asked her how it's going. She tells Bart that Frank had claimed his divorce was going to be finalized next week, but Myra didn't believe him because his wife is pregnant again.
She allows Bart to wait in Skinner's office unattended, where Bart then finds the key to the steam tunnels. Bart and Milhouse proceed to explore the tunnels and find the valve room. Bart turns the smallest valve, causing all the other valves to open in a chain reaction which fills the school with steam and results in severe water damage. Principal Skinner soon apprehends Bart and takes him to his office to be reprimanded. As Myra wheels in a television set Bart asks her to help him get out of his punishment, but she refuses because he wrecked her breakfast.
She was in the office when Bart sneaked past her to get into Principal Skinner's office to get all the teachers out of the school via the intercom.
Judging by how bad their relationship seems to be, it is likely that Myra and Frank are no longer together.