I wouldn't be hesitating, it's very very easy to report concerns to the OPG, they can be quite slow to move so the sooner the better, a quick email and it kicks starts their investigation.
As part of that investigation the OPG will automatically contact the local authority to ask if they know of her and if any concerns have been reported to them about the LPOAs so from that perspective the social worker doesn't need 'permission' to report to the OPG as the OPG will come to them for information anyway.
My manager would look at me as if I was mad if I went to them to question if I should have reported this to the OPG, it would be something I would be expected to do automatically and then just mention as having been done in my next supervision.
I would include the information that you believe it was a cold call type situation rather than a deliberate intention of your mum to make her attorney a long trusted solicitor for good reason.
Would you consider being her court appointed deputy for finances if the current LPOA is revoked? If not then the court may apply for the finance part to be passed to a court appointed solicitor.
it's unlikely they will pass on the health and welfare LPoA to anyone, that bit will probably just be entirely revoked.