I concur with SoberLeigh. With every script there is, or rather should be a pharmacy disclaimer stating something along the lines of..."if this px is required before --/--/-- please contact your Dr.
I would like to assume her Gp/Surgeon has not prescribed a repeat Px. You can call her GP all you like but they will not give out any info for confidentiality reasons...........on top of that, you'll only broaden the gap of your relationship. Ultimately though, having taken that amount of opiates in such a rapid time period means that shortly she will be withdrawing and crying out for more. This I believe is where you get to be one step ahead, pull in the reigns, address it from a subjectual point of view..........when she reaches for her next tab..........ask her to score her pain from 1-10........let her create her own chart........necessity (pain) over desire (addiction). She'll run out soon and hopefully before she does she'll be able to learn the coping mechanisms to take the medication for not it's desired but required effect.
I wish you and your Sister all the best.