There was just one photo of the signature here. I would also like to see the painting and the back of the frame.
You can use the Add Files feature to add more pictures.
Have to honest here, I am unable to find a match that makes sense. This artist did watercolor but the quality is not a match and there would be no reason for Frank to dilute his reputation by signing his wife's (poor quality) art.
I will opt-out and allow another expert to answer.They will see our conversation and your photos. I am not able to respond once I opt-out. Good luck!