I'm sorry, but I find this post very odd, something just seems off here. I reallly cannot believe that you are being so relaxed about this.
You discover large amounts of money in her account which you can't account for and when you confront her she lies. You then allow her to chill/nap even though she still hasn't come clean. Then incredibly, you give her the night to think it over, still not knowing the truth.
Sorry but you are incredibly naive. If she has got involved with the wrong gang you could find yourself with a brick through your window.
It's seems very odd that you do not want police involvement. I agree no one wants the police at their door, but tbf you have no idea what danger she is in. You do not know what other young girls, possibly her friends, are also involved or what danger they may be in, remember their parents may at this point suspect nothing.
It's all well and good taking the softly, softly 'understanding parent' route, but there are times when very swift, no nonsense action is required and this is such a time. Frankly it sounds as though you are more concerned about the stigma of your DD being spoken to by the police than you are about her welfare.
She will not be in trouble, she is a child!!! Your reaction to this is pretty underwhelming and the speed at which you have moved could have put others like her in serious danger. You need to wake up!!!!!!