Learn English – Difference between “had waited” and “had been waiting”

...had worked...

This is in the past perfect tense.

...had been working...

This is in the past perfect continuous tense. The latter means she had been working continuously with an advertising company for the past 5 years. The first does not necessarily mean her work with the advertising company was uninterrupted over the five years.

What would it be if you dropped the for/who from it? You would end up with:

everyone has been waiting

and

everyone have been waiting

Some indefinite pronouns, including everyone, are always singular, even if they refer to multiple people. So in this case, everyone has is correct. That means that

for everyone who's been waiting

is correct. (The verb goes with everyone not who.)