wlm doesn’t download all gmail messages

i'm using Windows 7, wlm Version 2011 (Build 15.4.3508.1109) and gmail set up for POP 3 account. All of the email to my wlm account downloads but some of my wife's messages do not download. They are in the google cloud since she can view them on her phone but they are not downloading to my desktop. Some days it works well and others not. I have restarted the program and the computer but it's not helping. We've been using wlm for years with mostly no problems but she has had this happen several times. I don't want to use IMAP.