i think my mom's losing it

my mom was dating a married man. he divorced his wife and remained with my mom for awhile until he said he fell out of love with her.

now she's driving by his house and overanalyzing cars in front of his house and things he's said in the past and his possible interpretations of her actions.

she called my stepmom, who my dad cheated on her with and then married as soon as they divorced, and asked for advice.

i think she's lost all rationality. what should i do?

(she already talked to a psychiatrist who did nothing but reassure my mom that she's a 'great lady' and doesn't need to contact him, hence nothing)