Sorry you may not want to hear this, but you are on the site posting for help. The others are right to "downgrade" the drug, but ultimately she will get addicted to the
codeine, also. Honest, downgrade as much as you can until you get her to a doctor. If she is unwilling, she has to be admitted to a rehab. If you are her boyfriend, and not husband, you have to get parental admission. If she does not want them to know, that's better help to convince her that she has to help herself, and not be admitted.
Try downgrading and get a puppy...(or kitten)...
Just try it for a while, if possible. A reason to be responsible for someone who may feel like they have no purpose in life may work...
It has for 2 of my friends...
And continue to be supportive, as you obviously are, and love her as much as you can. Give her another reason to be sober.