In this context, "if ever she" is really just the same as "if she ever":
If ever she stepped on her dog's tail, the dog would yelp loudly.
If she ever stepped on her dog's tail, the dog would yelp loudly.
Those two sentences mean the same thing, although the first has a more "poetic" or "literary" feel.
This is in contrast to the "if ever" in the expression if ever there was one, which is used to emphasize the truth about something:
If she ever stepped on her dog's tail, the dog would let out a loud yelp, if ever there was one.
In that sentence, "if ever there was one" underscores the loudness of the dog's yelp. That makes it sound like her neighbors could probably hear the dog howl, not just the people in the room.
اگرچه توضیحاتی ارایه گردیده است، متاسفانه هنوز تفاوت دو جمله مشخص شده را متوجه نمیشم.