We've been EC-ing (in a very slack way!) since B was 3 months. If I put her on the potty when I think she needs to poo, she'll generally do one - she strains too get it out too, but is happy afterwards! Sometimes we do still miss them though, so she evidently won't hold out for the potty if she needs to go.
If it will keep your little darling more comfortable for the next month, I'd start now. Is there any way you can potty her on the plane? Get a seat insert or something? Good luck!