You do have a point. She has no background in engineering and therefore no appreciation of maintenance and as the years added on the neglect became worse. The fact that the retail front made impressive gains does show where the focus was. She might be the immediate cause but the blame then has to be on the the folks that appointed her. GLC Boards are typically sinecures. Key appointments, targets and direction are typically set by the Holding company, in this case Temasek or the Govt.
I found it odd that the Minister of Transport is now setting the targets, bringing in people that are overseeing its delivery and the current point person. In the scheme things this is not good governance. With the PM's wife being the beneficial owner of this enterprise, no sure if the environment is right in the first place.