Based on the very, very limited information available to the public regarding this case, I have two (admittedly) speculative theories about what happened:
1 - The abduction was part of a gang initiation. The plan was to snatch a white female, hold her for 4-5 days, brutalize her, and then release her. SP was specifically chosen because one of the gang members knew her, perhaps perceived her as anti-Hispanic. They may have known each other in school, perhaps it was a mother daughter team where the mother knew SP from school many years back, the daughter was being initiated into the gang. Or, perhaps in light of the recent election, SP made what they perceived to be anti-Hispanic or anti-Mexican statements on social media, and hence the gang chose her as their target. Perhaps some combination of these factors.
However, the gang's initial plan had to change when this case quickly generated a significant amount of attention from authorities. They panicked. Now they had to come up with a "Plan B" on what to do with her. They had always planned to release her, but now they probably weren't so sure. Did she see anything? Could the authorities identify anyone within the gang based on SP's testimony? Had they really covered their tracks? And so an internal debate ensued over whether to release her as planned, or kill her. In the end, after a lot of internal discussion that went to the highest levels within the organization, the decision was made to release her. Perhaps accompanied with credible threats that any attempts to work closely with the authorities would result in serious consequences for her family. She was told what to say, and anything beyond that would would be a red line she should not cross, or else...
This explains the seemingly randomness of the crime, why she, specifically, was selected, and why she was kept for so long, at great risk to the gang, for so little benefit. And why her statements to date - at least those given to the press - have been so vague.
In summary, a gang initiation ritual gone wrong.
2 - I cannot discuss my second theory, as it is a clear and blatant violation of this site's current TOS regarding the case.