I still think it all comes down to explaining away having a knife and gun handy enough so that both are used to kill Travis with 2 minutes.
Here's a wild guess what she'll say. The knife was in the bathroom because Travis had used it there to cut the "bondage cords." The gun belonged to Travis. She doesn't know where he got it, or when, but she knows why he has it. Travis is willing to use her one more time for sex, but sometime after she reluctantly agrees to the sex- to sooth his temper--he shows her the gun and tells her he bought for self-protection.
She dropped the camera in the shower and Travis lunged for her. She grabbed the first thing she could put her hand onto to defend herself- and its the knife. Everything after that is kind of a blur- she couldn't process that he was trying to kill her, she acted out of blind fear, she isn't sure where each blow and stab took place- how could she be? Sobs. Mouthing "I'm sorry" to his family, or just saying it out loud, loudly, as she covers her face and sobs.
Shaking off the awful traumatic memory of Travis's deadly rage, she resumes. She does remember that he kept coming after her even after she stabbed him for the first time. and that somewhere, in the back of her mind, she remembered his gun. Afraid that he would use it against her if he could get to it, she stabbed him several times in the back near the sink, then ran for the gun.
At the end of the hallway, near his bedroom, she was holding the knife and the gun when he approached her. She used the knife as hard as she could because she had never used a gun before, wasn't sure if she could shoot it right, and he was still coming after her. She doesn't remember shooting him, but thinks that she was so shaken and still in such fear of him that she may have done that in shock, towards the end.
Something like that.