Hi, BrownRice, my completely hypothetical, but somewhat logical theory is that Jodi caught Travis nude taking a shower and used the camera as a ruse to explain her presence and catch him off guard. (Taking pictures seems to have been part of their love play.)
With him thus disarmed, she told him to wait a minute, retrieved a neighbor weapon, and then shot or stabbed him. (I always remember a film director, perhaps David Lynch, telling an interviewer that Hitchcock was brilliant because a person is never more defenseless than he or she is while taking a shower.)
In my imaginary scenario, she shot him first because she could it at a greater distance, thus not putting herself at risk from the much larger Travis. The blow partially blinded him and impaired him and then she, more panicked, went ballistic with the knife. I would think that a very self-possessed and possessed woman like Jodi would plan a one-shot killing, but also have a backup plan.
And, yes, the visit was apparently a surprise to Travis.