Seriously, this is church. It's more important to be able to communicate during your interviews what you did compared to the importance of any authorship. I know of some of my peers in undergrad who have gotten authorships, albeit 6th or 7th, for washing dishes or contributing little to nothing intellectually to the paper. I bet those people fare pretty badly when asked what they contributed. FYI, you can't make **** up.
Yes obviously here tiedeyeddog makes the most important point which is talking about what you did. Keep in mind if you did jack **** and got lucky and got your name on a paper, it will be revealed sooner or later.
I have put people on my papers that did NOTHING simply because authorship is generally up to the PI and I am cool with whatever unless I did 99% of the work and was put 2nd to last or something. Then I might have to make an appointment to talk about it and negotiate a better position or at least find a way to understand.
In any case, based on how well you can talk about a project you will reveal what you know and what you did. Simply reading a paper will NOT give you as much information on a project versus someone who actually did the experiments. The paper is basically a condensed version of MONTHS of work and only the good stuff. The bad crap, the reasoning, the design, the frustration, the experience...those you cannot get out of just reading a paper someone else wrote and you happened to be on because the PI is your daddy or something. We all know this is true because if you have ever read a paper you will see parts where you felt another experiment would support their point more, or that their discussion and experiments do not warrant their conclusion and what not.
On the flip side, I seriously doubt someone who has a dozen publications will not be able to talk about their own projects in a logical manner. Again, there are those special cases where someone held their hand and protected them from the rigors of research but for the most part most MD-PhD applicants will know what's up.
More specific advice to you here is to change your MINDSET. No offense, but you seem like you are in a hurry to get a pub and bail. Drop that mindset, do the work and you will be rewarded. Look at what your PI said:
She said: "low chance of resulting in a pub."
You immediately think: "ohh damn no pub will be handed to me...time to switch labs"
Wrong, you need to think like this.
She said: "low chance of resulting in a pub."
You immediately think: "ok low chance, but still a chance...I need to make this project better than she imagines it to be."
That is completely possible to do in your situation so make the best of it.