How to block a girl on Facebook?

[swEde?]

My bunny boiling ex-girlfriend with BPD keeps messaging me on Facebook but I can't block her. What she does is unblocks me to send me a message, then immediatly blocks me again, meaning I can't block her. Now last time I checked if you unblock someone you cannot block them again for 48 hours, so how is she doing this? It's really aggravating. Thanks guys
Please take the time to PROPERLY read my question please... that's 2 people already who haven't

[Oddblob]

Just unfriend her, then change your security settings so ONLY friends can message you

[Demonica]

Go on her profile on the right hand side theres a button click on it scroll down to report and click on the block button

[Angeleyes]

It's best to unfriend her, if she sends friends request just ignore it. Also change your security settings to friends only - who can message you. You can also go her profile and click block.