You do not need someone to accompany your mother. You may ask for within airport service if you book flights from Air Canada. You can tell Air Canada that your mother does not understand English and needs help for connection at Vancouver or Toronto. They may arrange someone to guide your mother to the connection through passport control and custom. There shouldn't be any problem. You may provide a notice for her to bring with, showing the procedure from China to Ottawa step by step and some English sentences she may need to communicate with others in both Chinese and English. There are always lots of Chinese on board in the plane from China to Canada.
