Thank you all so much for your responses so far. I feel so much better. And you are all right - I shouldn't feel guilty at all as this is a personal journey and it belongs only to me.
My sister is, for a lack of a more accurate (and worse) term, a snot. She is not overweight but she is the kind of person who needs to look better than everyone else. She enjoys being the 'thinner' sister. Yeah, like I said - a snot. So she would find any reason to diminish my weight loss and constantly remind me that I took "the easy way out" and didn't make a real effort. And so you all know - I DO NOT FEEL IT IS THE EASY WAY OUT AT ALL! In fact, this process so far has been harder than any diet program I have followed (or tried to follow) in the past. And there were many.
And if my sister knows, everyone in my family will know. Thankfully my mother knows what she is like so I trust she will keep it quiet. And my mom is being very supportive.