On page 1068 in NOAB5, in the footnotes Sweeney notes that "the narrative begins with reference to the Syro-Ephraimite War of 732-735 BCE." Referencing this event might give some reason as to why both Collins and Sweeney imply that the author might have encountered these actual events in their life. "Chapter seven is contained in what is known as First Isaiah. According to Sweeney, these include chapters 1-39.(1068)" I do not think that it is written in the time of First Isaiah because of the narrative voice of Isaiah. Chapter 8 still goes on with a very similar tone, but chapter 7 certainly does not seem that it would have been written by the same author as other books in First Isaiah.
As I read chapter 7, in the early verses of the chapter, there is historical information about Ahaz and Ephraim. Then we get to prophecies from Isaiah. It is interesting to note that even thought these are prophetical verses in Isaiah, I find it difficult to support that claim because it is saying you will do this or this shall happen to you. It is more of a prophecy than a retelling of an event that happened. The verses that do this begin on verse 13 and end with the next Chapter. Each part of this begins with "On that day." Verse 18, 20, 21, and 23 all have the same beginning. It could be this is a hopeful text of what may happen but it just doesn't seem that a writer would write in this context about a present event happening.