I agree with your advice, but this dishonest situation should not exist in the first place. If one person has friendship feelings, and the other has romantic feelings, then in most cases, the situation cannot continue - it's incompatible and will cause pain for both parties sooner or later. To put it another way - if one person has romantic feelings for the other, they cannot be a good friend because good friends champion each other's love lives and wish for the best - I seriously doubt a 'friend' that has romantic feelings for the other is rooting for her/him to be successful romantically. So it is inherently dishonest despite any good intentions between people.

If I found that a partner was knowingly in this type of situation, I would seriously question her emotional intelligence and wisdom. If she was unknowingly in this situation, I would gently point it out and hope she did the right thing and break off contact with her' friend' that had romantic feelings, for both of their sakes. If she didn't I would consider moving on to someone more emotionally mature.