curtj, without any real medical training I'd like to share my own experience. I tried gabapentin four separate times and got sick each time. My doctor suggested Lyrica and I took only ONE pill. Within a few hours I was so sick that my husband had to take me to the ER. I told the doctor there that I had only taken one Lyrica pill. He said (and I quote), "Well you took ONE!"...I also have Atrial Fib, similar to her Tachycardia.
I say all that to say that she should probably not take either medicine. I think that they are in the same family. Correct me if I am wrong on that. The only thing I can tolerate is hydrocodone, 5 mg, three times a day. A side note: I don't tolerate many drugs anyway, but that seems to give me almost no side effects other than constipation which can be alleviated by Senna tabs or a glass of prune juice. I even have recently had auditory hallucinations several times with the lowest possible dose of amitriptyline. I hope she can avoid these meds that make her sick. Our bodies are all different and usually doctors prescribe the most commonly used medicine. Maybe she, like me, is uncommon!