My sister is currently on Lithium Carbonate but she's being told she cannot eat many greens nor almonds?

She suffers from depression and was currently given Lithium Carbonate. While searching for certain food which may help with her depression - walnuts, herring, greens etc etc - she has found that many of the "brain food" cannot be taken while on Lithium Carbonate. Can someone please give in their two cents on this subject. I'm a firm believer that your diet - along with exercise - dictates your behavior so I recommended her that she eat healthier. Now that she has read all the interactions with great food we're not sure if how to go about her diet. Has anyone else experienced this? Will it really harm her to eat such vegetables or certain fruits while on Lithium Carbonate? Her doctor mentioned to not abuse certain food groups but she wasn't told exactly how much is too much. Any advice would be greatly appreciated. Thanks a mill.