https://www.aamc.org/students/download/271680/data/retestertotalscorechange.pdf
Let's actually use data for how people do on re-takes. Real data not something your friend did.
For people who scored a 21-32 on their first attempt: Around 36% scored more than 2 points better the second time around on average. 24% scored worse the second time around(which is definitely somewhat of a red flag) on average. So the chance of doing significantly better isn't outweighed much by the chance of doing worse.
For those who scored 21-23: To get to the DO average(27) would require scoring 5 points better(on average) the second time around: 18% did this.
For those in the 24-26 range: To get a 30 would require a 5 point swing on average. 15% achieved this.
Keep in mind in both cases the impact of a 27 or 30 would be diluted to some extent by having a poor score on their record from the first time around.
Bottom line: These significant improvements that actually make a difference happen less than people think. It's not just a matter of suddenly "Working hard" or "Trying".