Vayelle is not very strong in the One Power. Her level of strength is described by "The Wheel of Time Companion" as 34(22) which is a low/intermediate level in Aes Sedai hierarchy. With this level of strength she is unable to open alone a suitable gateway to Travel.
Vayelle is 86 years old and has been Aes Sedai for 44. She was born in 914 NE and went to the White Tower in 932 NE. After spending thirteen years as a novice and eleven years as Accepted, she was raised to the shawl in 956 NE.