This unfortunately can be a common theme in many households. Support from family and friends is a really important predictor of success with regard to physical activity and healthy eating habits. It can be very difficult for someone to develop and maintain healthy lifestyle modifications if they do not have a support system. However, if the client is in the action stage and ready to make behavior changes, you can help.
You can be an advocate for your client to develop healthy habits, and encourage altering some things in home environment. One motivational strategy is to ask your client to prepare her environment ahead of time to help trigger healthy eating or exercise. Keeping a gym bag ready by the door, preparing a healthy grocery list and meals in advance, engage in a group exercise class where the client will meet others who are supportive, etc…
Try to associate your client with other groups who have similar interests and goals of healthy lifestyles. It can be challenging for your client, but it can be done.
Best wishes to you and your client.