Show her possibly having insecurities about her looks, being the youngest in a family of guys/being overshadowed by her brothers, and all of that.
Harry would probably sound like the most over the top Gary Stu in the world.
Well, these two sound extremely annoying (I don't care if they are realistic or not), especially since in the OP you only mentioned the above stuff as the plot, so I thought they would be the focus. From your second post, I can see that's not the case, so forget what I said.
(And I agree with what you said about Tom. A relationship fic about the two of them would be the only Harry Potter relationship fic I would care to read.)