Assuming your kit is in the US, the email goes from your BES to US RIM to EU RIM then to her device using the local carrier (I have always assumed that is the case as I can't find a doc on it!).
Ok so RIM in the US _may_ hand it straight off to the US carrier for it to hop across the world but I can't see it, as which carrier would accept it without payment? I have always assumed RIM do the trans-atlantic transfer, then it goes to the carrier. I could be wrong but would love to know the real answer if I am
I have users across the globe on many carriers using many Exchange servers and just two BESs, US and UK. I never see any issues based on where you are or which BES you use (even though it's unsupported), except for the below, which sounds the same as your issue.
All my AsiaPac users are on my US BES using a mail server in Australias and all but one work fine. One guy has your "batching" issue (without the timestamp being the same) but as soon as I move him to my UK BES, it's fixed. This was on 4.0.7 and I am hoping my recent upgrade to 4.1.6 might help. It's an unsupported topology by RIM (as his mail server is in AsiaPac) so I just live with it for now as moving him fixes it. That said, your user just sounds like 50% of my users (roaming all the time) and they don't see the same issues. If it's only since the upgrade it might be worth using your post-upgrade support but a second BB over there would be perfect to test against first.