Hi and welcome. Sorry you found yourself here but at least you can talk to people who have been where you are at right now.
Listen to your brain. Trust your gut. What is the WISEST thing for you to do based on everything you just posted here!
Your girl is an unhealthy mess. What are your strong feelings for her based on? Do you think you can help her? Cuz it doesn't sound like she is bringing much to the relationship.... sleeps all day... cranky... been using heroin for years... in trouble with the law...
If she is lying to you (and that's what addicts do - they lie) you are headed for a world of hurt and nothing is worth the pain and turmoil an addict can cause in your life. Nothing. Especially after only 4 months.
You can't save her. You can't cure her. You can't help her. You can wish her well. And back away.
Take a wait and see on this. More shall be revealed.