I'm pretty sure they have to be fully vaccinated to compete. IMHO Flu vacc is even more important than Tet, competing - wise, as Tet is not infectious and Equine Flu definitely is!
Most county shows do require the horses to have up to date flu vacs, some will never check but others are very strict and you will not be able to enter the showground without a check. If you qualify for a Championship show you will need them done also so its not worth starting the season without getting them done.
you need 3 injections but tbh she should have had it already as a flu is compulsory for competitions - and is just unsafe not to have done it. have you not done any local comps or going straight in at county?
Ie. first 2 and then the 3rd later, I think its 3 weeks between the first 2.
I was planning to have her done so she falls in line with my other horse which meant first jab in june and as she doesn't go anywhere (shes only 2) It didn't matter but now am planning on devon county so different case. Would she be covered witht he first 2 jabs only by then?
You have to be fully up to date with it annually [Not even one missed by a day anywhere in previous years] or have at least the first 2 done if a restart if my memory is right.
You only need the first two before Devon, if you get going quickly the third could be done in July and will be the one that is her annual date which by next year could be done with your other horse thereby saving 2 vet visits, if you did not start til June they would be way out of sync.