It seems she can't get enough of that book...
Rainbow Dash: What? Twilight! What are doing? Don't tell me you brought your books here with you?
Twilight: Yes. I can take some sun while relaxing by reading. I like the beach for that.
Rainbow Dash: But, there are so much activities you can do around here. Don't tell me you'll stay there all day, reading?
Twilight: Yep! I'm not very good at beach sports anyway and I'm going to study the ocean tomorrow with my reference manual and Fluttershy.
Rainbow Dash:..... Egghead. Come on Pinkie Pie, let's build a sandcastle.
Twilight: If you want a book for learning to how build a big one, I have a very good one in my....
Rainbow Dash: No thanks!