During the reign of Alexander III, marie feodorovna had obtained from her husband to keep the crown jewels at her home (the Anitchok palace). It would permit her to avoid the discomfort of asking them to the Court officials every time she wanted to wear them.
When Nicholas II was propelled onto the throne, his mother refused to relinquish the jewels, which belonged to the state and by right were worn by the reigning empress.
it seems that the roughness of the relationships between the two women came from their big differences of caracters and behaviours, Alexandra was said too "puritan", haughty, prudish, snobbish, and empty of charm. She disliked the society of St petersburg while Marie feodorovna loved it. Add to this that Marie Feodorovna was a possessive mother, and she wanted Nicholas to be with her the most of the time.
So it would have been difficult for them to get on well. They were too "exclusive". it seems that the strains began just after their wedding when Nicholas and Alexandra were forced to live with the empress dowager. it also seems that their lack of sympathy lasted all their lifelong, and became deeper during the time of rasputin.
