It would be far better to find out what's actually causing the constipation. And if the current vet can't help - switch!! Especially if this is causing her actual pain. Dogs are not normally constipated (obviously!!), and this needs sorting out - even if it means gradually switching her diet, if this is what's causing her problem. I'm just wondering, given the breed, whether she actually has a blockage (Goldens, and Labs CHEW) and if so, this is serious.
Add Do NOT give her any form of laxative without finding out exactly what's causing all this and only on the advice of a vet - you could do more harm than good, especially if there is a blockage.