Sorry to hear that, and it shouldn't have been a favour they were doing. She paid for that stuff and it is
supposed to be available, always. It's hers.
In my experience, it has always worked as expected. Just recently, I realized that 2 albums my wife had worked on weren't in my library - I had purchased those way back in early 2010, on my last PC. I logged into the store and it was still all on the cloud for me.
As a matter of fact, even the The Cure singles I bought in 2008 - that the PC before my last PC before I switched to Mac - are still right there.
Recently, I've started replacing iTunes albums with ripped CD versions in 16 bits, deleting the compressed version. Ever since, when I hook up my iPhone to my Mac, I get a prompt telling me that I have some purchased albums on my iPhone (the compressed iTunes versions) which are not in my library and asking if I want to import them in my Mac's library.