When a female has a strong sense of admiration and respect for another female. Said female often idolizes the other one. There are generally no sexual or romantic feelings linked to girl crushes. The "girl crusher" may simply wish they were friends with their girl crush.
The "girl crusher" may think the girl she is girl crushing on is,
f) some/all of the above
See Jenna Marbles' video on girl crushes for more information.
Person One: "Kayla just adores Emma Watson. She has a poster of her in her room, has seen all of her films and even had her hair styled like Emma's at one point. I heard that she's considering studying at Brown University as well."
Person Two: "It sounds like Kayla has a massive girl crush."