Khawla Barghouthi, 20, of northwest London, Rizlaine Boular, 21, of central London, and her mother Mina Dich, 43, of southwest London, appeared at Westminster Magistrates' Court on Thursday, the Metropolitan Police said.
The three were arrested last month.
Britain has been on its second-highest alert level of "severe" since August 2014, meaning an attack by militants is considered highly likely.
There'll be another hearing on May 19th.
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