i really don't think my best friend will be angry,but i'll g

i really don't think my best friend will be angry,but i'll go and see her,in case she is.in case后加的从句不是用虚拟语气吗?in case后的从句用虚拟语气，应该用in case she should be，而我想说的是in case 后为什么用is？