Interesting question. Your example would work grammatically, but it wouldn't sound as natural. Think of it as present tense. We use present simple tense to talk about future FIXED events. "The plane leaves tomorrow at 8:00." Or, "We have exams all week next week."
"Have got" is another way to say "Have", don't think of it as present perfect. (It's a very British way to say "have".)
It could also read, "She'll go crazy when she finds out we have exams in three days." (That would be more of an American English way to say it.)
Hope this helps!