Management experience

I am going to share my recent experience of managing and will be happy to get your advice. In the company where I work, when our manager is absent for some reasons then her assistant is in charge. And when it happens that they both have to be absent then I am the next one who is in charge. Last and this week I’ve been experiencing “managing,” as I’ve been in charge during this time. On the one hand I like my co-workers and I am on good and friendly terms with them and want to stay that way. But I am also a responsible employee and try to do my best at work. During this “managing” time, I noticed that one of my co-workers and a friend was a little “idling” and at first I didn’t do anything hoping she would understand. But then I asked her which I believe was in a nice, not official manner, more like to a friend, suggesting that may be she should work on something that she had to do. She got offended and was trying to avoid me the rest of the day. I actually tried to protect her as well as myself because there is someone in the office who always “reports” on someone. I thought it would be fair to tell her personally rather than pretend that I didn’t see anything but to say about this to the manager. I hate lying and I don’t do it well. I didn’t feel that I was lying when my manager called later asking how the things were going on, and I told her that everything was good and everyone was working well. I could say it because it was actually so. Did I act right or what was a better choice to do in such a situation?