Hi Mona,
When we have had a thrombosis the risk for relaps is increased because the walls of the blood vessels are damaged. Hopefully your mother will be able to continue EPO treatment.
Everything that can increase the risk for thrombosis like flying can be dangerous. There are many ways that you can try to avoid thrombosis during flying like having special stockings, moving, drinking fluids and so on:
http://airplanes.suite101.com/articl...sis_on_flights
Kind regards
Birgitta-A