Defined Benefit Pension (old Pi/us Pension Plan)

[AAflyer]

My wife is a former PI/US employee with service under both the old defined benefit pension plan which PI (and I think US until early 90s) had for CS types as well as the newer defined contribution USAirways pension plan. She had to leave US, because work conditions, salary and benefits were becoming very bad (except, of course, for the Wolfman and his trusty sidekick Rakeesh (sp?), but that's a whole other story!). US, of course, never sent anything in writing confirming her departure, but I never found their HR staff to be super efficient anyway. My/our question: Although she is nowhere near retirement age, she is vested in the US pension plan, which includes the old (and superior) defined benefit plan. How does she go about applying for benefits under that plan when the time comes? Wasn't US legally obligated to inform her of her pension benefits and how/when to go about applying for them at age 55/62/65 whatever? We realize that she won't be entitled to health/dental insurance, travel benefits, etc. but her 20+ years of service is worth something, legally speaking, in terms of a monthly pension amount, piddly though it might be.