why did this girl I meet block me on Facebook when I added her?

[DaZzl!nG P!Nk]

well there may be some reasons:
1) did u tell some thing that made her kinda upset? try remembering every thing u talked about.
2) some girls get upset when u talk about bf/gf and stuff like that with them.
3) maybe she didnt enter her own fb. (hack ,...)
4) or maybe when she wanted to accept ur request she accidentally chose "not now".
5) some one forced her to do so. i'm not sure about this actually.
6) try asking a mutual frnd about it. like: i sent her a frnd request but she didnt accept. do u know why? can u ask her?
No dont ask her face to face. she may not want to tell u the reason.

best wishes