Stand up straight! Look brave!
(Stand up straight! Do not show fear!)
(In fact, the version with tìtstewnga' is grammatically correct. However, in the context in which Varang speaks it, the original version is justified, even if it bends the rules. She wants to say something sharp and punchy, with good rhythm. 'Ur fkivan tstew! is much stronger than 'Ur fkivan tìtstewnga'. And it's perfectly understandable.)