Glad you are back!
No contact means no contact. The response "can I contact you via text" is a further manipulation to lock you into continuing to respond I hope that you see that. Understand that if the only response they can get is negative that's ok - its a response. Next would be "well I won't text but if such and such happens I will let you know", or "would it be ok if just every once in awhile I check in on you"? blah blah blah. She is the hook and you are the fish.
As for feeling like you should have responded and were rude not to do so this is co-dependent thinking. You DID respond. I am sure your ex understands the meaning of no contact and there is no need for clarification.
As the codie in the relationship the best you can do for your addict is to no longer enable. While you feel a guilt because it "wasn't her fault you became addicted to her" - well that is rationalizing that you owe her to remain in contact with her. You do not. What you do owe her is not to enable her addictions - because it only perpetuates it. No contact seems rude, or hurtful, and possibly hateful. Its not. The best we can hope for as far as they are concerned is an accountability for actions. When we are co-dependent and enabling we absorb all of the addicts accountability. Whether she ever feels this way no one can say, as long as she is actively using she probably will not.
One day at a time my friend.
Now, what are you doing for you to heal from this?