Your "gut feelings" haven't let you, or Lyla, down yet and I have no reason to believe otherwise in this case. You've developed a wonderful relationship with Laurie and I'm sure she'll recognise that you only want what's best for Lyla.
Maybe when she's back from her course you could invite her out one evening for a meal and a chat about Lyla. Probably not the sort of thing that you'd normally associate with a normal vet/client relationship, but it seems to me that you two have progressed so far beyond this already in your mutual desire to do the best for Lyla that it would do no harm at all and would provide a more relaxed environment for the two of you to have a friendly discussion.
I'd look upon the text message as a sort of holding action until you can get to speak to Laurie and maybe she'll be able to recommend something that'll ease things a bit for Lyla until you're both able to have a long chat about her treatment.
As to the Gabapentin, I was prescribed this some years ago for post herpetic neuralgia following an attack of shingles. Did nothing to relieve the pain but the side effects were rather nasty with me staggering about and bumping into everything, with not a drop of whisky past my lips

Bob.