I hate to say this, but she may have interpreted that "I'm sorry" to mean that you are sorry for doubting about Jehovah--thinking that you acknowledged how you wronged HIM (not her) and that, while you may be spiritually weak at present, in time...and with that repentant attitude...you may increase your spiritual focus again. [meeting attendance, ministry, etc.] She may be entertaining equal hopes for your return, just as your hope for her is to remove the wool from over her eyes and to free her to leave.
I only bring this up because if things progressed with the two of you getting closer under such a [tragic] comedy of errrors, the pain and dizzying shock of it would be that much more intensified if discovery led to a reverting to your former estranged state. In other words, enjoy the renewed connection, but try to discern (discreetly, of course) if she is still placing conditions on your association with her, and if those conditions are ones you can comfortably meet with. [and vice versa]
That having been said, I'm so happy that you have found your sister again! Good for you. And, especially, good for you for being proactive and mature in taking the first step.