TL;DR: If you can publish a few-year-old unpublished paper, your contribution definitely deserves co-authorship.
However, you will find that the actual work will soon exceed adding citations, and changing format. If that were easy, your advisor or her previous student would have done that few years ago. This may cost you months.
When you add new citations, the least you need to do is to add more discussions in the related work. After 3 years, there would be a lot of progress in the field, will the technique in the paper still state-of-the-art? How it compare to the papers from last years etc? You may need to do more experiments to compare with the new techniques. This often means you have to do all experiments in the paper.
Changing format may not be enough, you may need to change the narrative to fit the theme of the conference. Some conferences require particular sections, e.g. Threat to validity, etc.
The conference may adopts rebuttal phase, conditional acceptance etc etc. Handling all these costs a lot of effort.
Since it has been abandoned for a long time, this is likely not a great paper. It may be rejected the first time you submit, and maybe more than one time. I'm sorry but this is the truth :) It may take you a lot a lot of effort.
You don't have to worry if you deserve co-authorship, if this is what bothers you. Instead, you should worry if you can actually do it.
Like you and Kbreto, I was asked to do the same task during my PhD. I refused to do it :) The paper my advisor wanted me to work on was in a good shape in term of format etc. But it had been rejected a couple of times before. I thought that it would be easier for me to do my own research and publish it, rather than trying to save someone else paper.
Fast forward 5 years, that paper is still not published, and I don't think it will ever be :)