A 4 year old, eh?
Well, bug's land might take the whole day.

Especially if you are going at a warmer time and let her play to her heart's content in the water play areas. Though you might want to see my September trip report for pictures of what can result from the water play, and helpful "what clothes to bring" hints.
Oh, and Monster's Inc is a super-cute ride that she might very well adore, and if she's like my guy she might want to go on again and again.
Others might have a different feeling, but to me, the "lands" at DCA aren't like the lands at DL. They are spread out, but they don't feel separate. Well except for bug's, but that's b/c there's an entry area and it dead-ends.
But to me, Tower of Terror is over in TOT-land, lol, Monster's is in the same area but doesn't feel related, it's just where Monster's is. And so on. It's just so spread out, even inside of the lands (except for bug), it doesn't feel to me like you're inside of a land like it does, to me, like at DL.
And just in case you haven't heard this, the height measuring stick for Jumpin Jellyfish is rumored to be very off. So if she's just at 40 inches, even if she measures OK for other rides, she might not measure up to that stick. I find it a good idea to take EVERY ride, no matter how many times you've been on it that trip, as a "let's see if you can go on the ride this time!" moment.