It’s the LAs responsibility to oversee the implementation of the EHCP and as such I would expect the LA SEND officer to be involved when there is a need to coordinate health, social care & education to make a change to a plan. Does the child need to see an EP again to get the plan updated? Could you request a re assessment with all agencies involved? It’s rare, but possible.
The LA can commission all sorts of services, and often magically find the ability to do so once tribunal proceedings get under way, which t is likely if the plan isn’t amended and mum wants it to be.
If CAMHS refuse to see this child on the grounds of the medication, have they or might they have raised any official concerns around the prescribing ie safeguarding referral?
Are IAS supporting parents as this often makes a difference to how Interested the LA are?
Do you feel this child is able to cope with school or does the pupil need alternative provision for a time? This could be commissioned by LA if available locally, or paid through existing EHCP monies.