Mom was prescribed xanax (alprazolam) for her anxiety. but i thought that ssri's are usually the 1st line of treatment and benzos only given if ssri's dont work?

Different doctors: prescribe differently. I use SSRI's initially when I can but if a person has truly debilitating anxiety - I may prescribe short-term benzodiazapines initially. I might also use short term benzo's if the person is initially feeling more anxious as a side effect to their new SSRI. Some doctors are more liberal with benzos than others.

Panic: Some doctors use benzos either with SSRIs or as first line depending on severity of panic attacks, with use being on temporary basis.