a = '"ONE" # "TWO" # "THREE" # "FOUR" # "FIVE"'
b = '"NANA" # "PAA" # "THREE" # "ELI'
a_elements = [key.strip() for key in a.split('#')]
b_elements = [key.strip() for key in b.split('#')]
filtered_b_elements = [key for key in b_elements if key not in a_elements]
new_b = ' # '.join(filtered_b_elements)
Удалить строку из другой строки