The principal benefit of having an SLP work in conjunction with decoding/encoding intervention is that they can give more specific instruction regarding the exact oral-motor sequences that generally produce certain speech sounds, and then directly tie that to the graphemes, so that even if the student can't quite generate the correct sounds, they have an additional (oral-motor) tag to connect phonemes to graphemes. And sometimes it even helps their articulation. A lot of learners reach a point where they are stimulable, but have trouble re-training old habits, which is partly an automaticity deficit. (Not an SLP, so I'm getting a little out of my range here, but this is what I'm told by my SLP colleagues.)
Whether your DD would do better with an SLP or LD learning specialist managing AT isn't clear cut. But if you've maxed out on whatever she had before, then it probably wouldn't hurt to have someone with a slightly different angle try. I've had building AT specialists who were SLPs, and were very successful with students of a wide range.
I'd also comment that I actually have seen students whose spelling improved after adopting routine AT, as they were now consistently seeing correct spellings (vs their own questionable spellings), so even if they continued to struggle with phonetic decoding/encoding, at least their visual memory of correct spellings was being reinforced. It's not the most efficient way of learning spelling for most people, but the learners we're talking about aren't most people.
For streamlining AT, when generating written responses, I usually recommend speech-to-text for first drafts, then editing and revision via keyboard/wordprocessor (with spell/grammar/style checkers engaged, and thesaurus function). For note-taking, it depends on whether she's taking notes from a lecture with/without visuals, with/without diagrams or symbols, in what content area, etc. In the classroom, I would also suggest accommodations that are not solely AT, such as teacher-provided electronic notes (skeleton during class, and complete provided after class, so that she adds some of her own notes in real time, but doesn't have to worry about missing anything, since the complete notes will be available after the fact). If you have SmartBoard or similar technology in the classrooms, the teacher can also print screenshots of the board as s/he goes along, and provide those as a copy of complete class notes after each class. Or if no SmartBoard, your DC can be allowed to take photos of the board on whatever approved digital device she has with her.
