You should have Ginny ally with Harry even if you don't plan a romance between them. Interesting what you have so far.
Author's response
I don't think a possibility for an alliance is going to happen after fourth year, because that's when Harry closes up to just about everyone except Myrtle.
Also, there's no basis for him to even start a friendship with Ginny aside from the rather small interaction he has with the twins in third year, and I'm of the opinion that if it weren't for his friendship with Ron, Ginny would not have even been on his radar.