Rescue Remedy is useless - Might be worth trying something like Oxyshot or something stronger, and I'd also "test" it before as not all calmers are effective for all horses.
the nettex carl hester one is good and you can get syringes of it so you dont have to load it up over time -my friend uses it on her dressage horse before comps as it is a loon but since using it -she swears by it - she tried oxyshot too didnt work for her though