The tweet is gone now. Thankfully the Wayback Machine crawled it but it's not always guaranteed.
Ver archivo adjunto 4254315
(archive)
Next time, remember to
ARCHIVE EVERYTHING.
As for the tweet itself, this is a retarded argument to say the least. At no point did Slenderman actually cause her to stab her, it was simply a justification she made up in her mind because she was mentally ill. People stab others and say aliens made them do it all the time, that doesn't mean fiction affects reality that just means somebody was retarded.