Constipation

My daughter has really struggled to do a poo now for a few months. I’ve tried all the various foods people suggest to get the system going but nothing seems to work. At best she poos every other day but more often than not, it’s only twice a week. I went to the doctor and have been prescribed Movicol. I’ve been using it since Sunday and still no poos since Saturday. My daughter tells me her tummy is sore but she just does not want to poo. She paces around until she physically can’t hold it in any more. I feel like it is definitely a mental block rather than a physical issue as her actual poo, whilst mostly solid is not what would typically be described as a constipated poo. Has anyone else been through anything similar. I think it all started when she unexpectedly did a poo on a potty about 4/5 months ago and I think it really scared her? Anyone have any tips to remove the mental block? We’ve always been very open about going to the loo and she’s often in the bathroom with me when I go for a poo. I’ve tried looking at books about pooing but nothing is working. We’re hoping to potty train over the Easter weekend, but I feel like she needs to be more comfortably pooing before we can attempt it? Thanks in advance.