@Cjscott323,
You've caught her in lies before.
Decide whether you can live with those lies, or not. Talk to your girlfriend about your concerns.
And it might not be a bad idea to make some sort of a plan when it comes to her son and money. You can, possibly, create a bank account for him with some agreed-upon monthly amount in it as the maximum and then she deposits into it, up to the max during a month but no more. That way, it's above board and her son (maybe) will learn how to budget. It doesn't have to be a lot; I'm not suggesting you and her start paying his rent or anything. But if she slips him, say an average of $80/month then make it an even $100.
And if she goes over, then it's time for a nice chat again.
Oh, and stop snooping, not only if you want to keep her in your life but also if you want to keep anyone in your life. Snooping's just a bad idea all around.