My sister is 5'1" and 105 lbs. What size board would be best for her? I was thinking a 125 or 127, but not much of those out there. She is a beginner, but I think she will advance quickly. Any suggestions for boards or on size?

you can have her try 125 or 130 hyperlite eden, 128 hyperlite divine, 130 liquid force angel, 131 liquid force diva, just to name a few. you should look for a beginner board or maybe a beginner/intermediate.