Without making it a tirade again, or personal, I'll summarize.
IMHO
"She was only doing what she was supposed to do" is a crutch. It's a coach's crutch that generally means either, "I don't know the rule and don't understand this ruling." or "I think that rule is unfair". It's an umpire's crutch that often means, "I don't know the rules, but this ruling SEEMS right."
I would say that at least 1/3 of the time someone says this, they are wrong. The other 2/3, they happen to be right, but only by sheer luck. Generally, to me, if an umpire says this, he is as much as saying that he doesn't know the rule involved, and is ruling on what he perceives as fair. I'd rather umpires know WHY they are making the correct ruling as much as I want them to make the correct ruling.
Case in point - the OP (and please don't take this personally). You had the rule right - but only on accident. You made the ruling because "I feel like the runner was doing what she was supposed to do", and in this case, the ruling was right... but to me it's important that you rule the way you did because you KNOW the relevant rule. If a coach asks you about the call and you use the crutch, he will know you don't really know the rule. Much better for blue to say, "In ASA, the runner is not out when she unintentionally interferes with the ball or the fielder making a play while she is standing on the base."
So much for making it short, eh?
Anyway, that is the background of the sigh ... I hope you don't take it personally, but I also hope you (and all umpires) shy away from using the phrase, or at least, if you find yourself thinking that phrase, you will later check the book to see not only IF you were right, but WHY you were right.