Cavandra is not very strong in the One Power. Her level of strength is described by "The Wheel of Time Companion" as 31(19) which is a middle/low level in Aes Sedai hierarchy. With this level of strength she is unable to open alone a suitable gateway to Travel.
She was Tylin Quintara Mitsobar's advisor before leaving her to go back to the White Tower after the new Amyrlin Elaida summoned her. Cavandra had been advisor also to Tylin's father when he was king of Altara.
Cavandra had gained a limited influence since she had been advisor for so long, despite the rulers of Altara not being very powerful and influential.