If she is doing whippets, then she is not sober. She's learned the right words to say. They are teaching her the phrases of recovery in her rehab. Just because she can say the right words, it does not mean that she is serious about recovery. My addict step-daughter knows all of the right phrases. She has been in a couple of rehabs, and has been to NA a few times. However, she continued to not do the work to get sober and she relapsed. That's why you have to watch the person's actions, not just listen to their words. My step-daughter was telling us she wanted to be sober, but was still drinking and blaming all of her problems on other people. It wasn't all that surprising when we heard that she was back on heroin.
It is good that you are getting help for yourself. You can't change your gf, but you can make a good life for you and your son. The most important thing is that your son is safe and that you can be there for him.