I frequently travel all over the map, including between the US and Europe. There have never been problems with sending or receiving emails (I use gmail and my academic email in the US) per se, but the quality of local internet services can vary a lot and that can make communication more difficult. What is more a factor is the time differences. Also, if your T is on vacation, I would be more patient as she may not really want to work much during that time. Maybe read your message and will respond when she can or when she is back home?