The fact the child reached 15 months without mom seeking medical advice tells me that she is still in denial - like ok we take the tube, we go home, and life goes back to normal. This is a really big deal and only the start of a very long process that little girl is going to face. There may already be some brain damage from lack of nutrition meaning the brain never catches up to what it's potential could have been or they discover down the road there is a genetic condition responsible for the issues. By encouraging mom to go to a daycare centre where there is help may be the best thing you can do for this child.