Further to my last comment, a subpoena was issued but there was no attempt to serve her with it. She happened to meet some police officers she was friendly with 2 days before the hearing, and she cooperated with them voluntarily from that time until she was jailed. See paragraphs 228 to 238 of the trial judge's ruling:
https://www.canlii.org/en/ab/abqb/doc/2016/2016abqb706/2016abqb706.html?resultIndex=2

Also note, the defence did argue that the witness's testimony was tainted by the appalling treatment she had suffered during the preliminary hearing and should be dismissed. In this case, the trial judge ruled against dismissing the evidence -- but surely it should worry any reasonable person that such a gross failure to ensure the rights of a witness comes with its own dangers to the integrity of the case and the ability to prosecute.