Mental health is a complicated subject. There are many different conditions present in varying degrees. Plus it is possible for a person to suffer from more than one at the same time. It really takes an experienced professional to sort it all out. Even with the best of intentions, it is possible to cause considerable harm by telling her, whether you are right or wrong.
Many members have told the pwBPD in their life. There are a few success stories however they are dwarfed by the number of stories where doing so caused things to become much much worse. It is impossible to know and since the odds are really against doing any good, I would recommend you keep your knowledge to yourself.
Here is another resource on this.
Workshop - BPD: How can I get someone to see a therapist or to get into treatment? I would suggest you start posting on board for coparenting to get some answers and support for your child.
Raising a child when one parent has BPD board If there are legal issues then we have a board for that too.
Leaving Board: Family law, divorce and custody
