The purpose of editing is to clarify or otherwise improve a post. Feel free to add citations and attribution when it is clear what the probable sources are (e.g. a direct quote containing many words). The appropriate mechanisms for noting unproven but suspected plagiarism are comments to the suspected plagiariser and, if necessary, flags to moderators. You didn't specify which posts you were referring to, but if they are the ones quoted below, you might want to rethink your claim to priority.
Based on @Mitch's link, I gather that these are the sentences you're referring to, quoted verbatim except for line breaks and other formatting:
Yours: A better expressions would be "My aunt/uncle and her/his family" which implies my aunt or uncle and their immediate family. You could use "mother's family" or "father's family", although this could refer to their parent, grandparents etc..
Hers: On a second note, you might consider — my aunt and her family or my aunt's family. Personally, I like the former better: Today I toured around the city with my aunt and her family who came to visit me.
The question you were both answering was:
Word/phrase to unambiguously refer to “aunt, uncle, and cousins”?
The concept of naming a family member and tacking on "and family" is a good idea, but it's possible that she came up with the idea independently.
If you move your mouse over the post's date, a tool-tip appears with the time stamp. Based on this time stamp, we can see that your answer came earlier. However, the following quote from Mitch came even earlier than yours, and mentioned the same idea. Perhaps you should credit Mitch for the original idea.
Mitch: Right...it seems like a reasonably common concept, eg visiting the nuclear family of your aunt.
It would appear that all three of you came up with the same idea independently (and I saw at least another further down the comments to the question). It would be poor form to claim attribution in the later answer when you didn't attribute the earlier comment.