@feha
Seeing as I know this kind of thing happens, but I have no examples off the top of my head, I shall instead defer to Wikipedia.
"While these honorifics are solely used on proper nouns, these suffixes can turn common nouns into proper nouns when attached to the end of them. This can be seen on words such as neko-chan (猫ちゃん) which turns the common noun neko (cat) into a proper noun which would refer solely to that particular cat, while adding the honorific -chan can also mean cute".
Yes, honourifics like -chan are mostly used with names, but not only with them.
The meaning of the title is relevant, because you've got to consider that this is a Japanese manga aimed primarily at a Japanese audience. And when the Japanese audience sees 見える子ちゃん what would they think of it? It's the equivalent of an English audience encountering a story called "The Girl that Can See". Are you saying English readers would think the protagonist's name is "The Girl that Can See"? While it's not impossible in Japanese that the author would have her actual name coincide with her description, seeing as we've been given no indication of such fact I see no reason why one should believe that. The fact that an (unofficial) translator decided to keep the title as Mieruko-chan instead of translating it hardly means anything about the author's original intent with the title.
You're free to believe what you like about her of course, but you shouldn't be surprised if others -including the translator to whom you were originally replying I just realised- don't see it that way.