Well, I don't think it is an immediate iterpretation of Maka, The book is testing her Soul too. So I think it just took the necessairily random character that came in handy for making Maka jealous. And now that I think about it, it's kinda weird that they didn't began(or it happens soon) with school notes or something....seems Soul is the harder weakness(we'll see) And that while she hasn't even realized that she likes Soul according to her sex change!(but I understand it if Ohkubo just CAN'T draw her looking like Soul XD)