As Crystal Empire affiliations with Equestria are not clearly defined. I can not justify any offensive strike against a potentially neutral country.
However defensive security measures would be established as contingency plans for the possibilities of a Crystal Pony threat.
However the Crystal Empire is noted as being highly isolated in the tundra of the frozen north.Making the seizure of Crystal territory a near impossibility.
However any attempts by the Crystal ponies to reinforce Equestrian lines could be easily routed by coalition forces.