Quite! It is the solicitors' job to ensure disclosure is handled properly. They have a duty to explain to the client what disclosure means, which documents have to be disclosed and, crucially, that unless privilege bites, all relevant documents must be disclosed even if they are unfavourable to the client. They then need to check that disclosure has been carried out in accordance with the rules.
I suspect Counsel was guarding her relationship with those instructing her when she said that it was the fault of the lawyers, and thereby including herself in the default.