I'm not familiar with Synacthen(R) Depot.
Generally an attack that last for more than 3 days (depending on severity)...her neurologist should be contacted as a course of IV steroid may be required plus it should be documented in her chart as this is a way for MS to be tracked.
An attack can last for a few days to months so it is important for her to be evaluated as soon as possible.
~Zig