It was only sheer luck (good or bad) that she was out there on leave. They can't have planned for that. If they have an agenda, picking off Jedi when they happen to enter the area isn't it- even though it is clear that they aren't scared of taking them on!
The Cult are trying to do something and this attack was something to do with that.
Curious...
Marcus dealt with Sareena's trail, but they did not attack with the intent of killing/capturing her, as you say. Perhaps they attacked to wipe out the passengers, but they do that anyway, so I'm discrediting that...
One of us, not me, investigated the cargo hold. They removed a bunch of agricultural equipment. Could it have to do with the gumf they stole?
I need to hammer in the point that the Cult are REALLY not like that. They are not interested in spite- in fact, they dislike emotion. They are intensly practical; the reason they slaughter people is for efficiency- it's cleaner that way and they don't care about life. But they have nothing to gain simply from death.