is any cheaper way that she can go?
Definitely
Cheapest way would be actually via Brussels, Cologne and Warsaw, since German railways (
http://reiseauskunft.bahn.de/bin/query.exe/en?newrequest=yes&protocol=http:&) sell discounted tickets London-Brussels-Cologne (seems like not a problem to get it for 69 EUR if bought some time in advance), they also sell Cologne-Warsaw for "Jan Kiepura" EuroNight train (seats as low as 29 EUR). So basically you can leave London 14:34 and be in Warsaw next morning for less than 100 EUR. While Warsaw-Olsztyn even standard fare bought before departure would be from 44 PLN (app. 11 EUR)