Doesn't NYU place like 60% biglaw? Doesn't that mean that roughly one in five students below median land big law there? If so, her story may simply represent the fact that some firms are willing to reach deeper at CCN level schools rather than any secret sauce to getting biglaw when you don't have the grades.
In terms of the way you phrased the question ("do interview really care more about tenacity than grades ..."), the answer is absolutely not. You can be as bold, confident, and tenacious as you want, but if you have shitty enough grades, or go to a shitty enough school, the odds are outrageously stacked against you. And, vice versa, if you have stellar enough grades at the right institutions, it almost doesn't matter how you present yourself or how imbecilic you are. Grades > tenacity.
But as far as what to do as median at CCN who wants biglaw, I imagine the three following bits of advice shouldn't be controversial (obviously I encourage more experienced or informed people to chime in):
1. Bid wisely. Your grades should meet, or preferably exceed, the cutoffs disclosed by the vast majority of firms you interview with if not every single one. Don't waste bids thinking that you'll wow screeners with your personality and get them to waive their grade cutoffs.
2. Use this summer (assuming you're a rising 2L) to network, hustle, and mass mail. There was a guide written on this board at some point about hustling your way into a biglaw job. A dude with not-so-stellar credentials ended up getting a bunch of offers by being a beast networker/hustler. My guess is that he was a bit of a social badass, but it's still worth finding and looking at that post and others like it if you can.
And I would definitely start mass mailing before OCI. Once OCI begins, mass mailing becomes much more of a shit show. FWIW, I was top 5% at a T25, I mailed around 100 firms during OCI (all with at least slightly tailored cover letters), and I heard back from one firm. Don't get your hopes up about mass mailing, especially once OCI begins.
3. Work on your interview skills. If your school offers mock interview opportunities and the like before OCI, take them. Be aware of how you come across to people and try to improve your social/interviewing weak spots.
And yes, I'd agree with your friend that you at least shouldn't apologize for bad grades. Not that there's any secret to that--I just think acting butt hurt about your law school performance won't make you fun to talk to.
Sometimes, when trying to figure out how to best answer certain difficult interview questions, I found the following thought experiment useful. Imagine that your school contacts you and asks you to interview potential incoming students for next year's 1L class. You ask them the question (or some analogous question) that you're wondering about. What would strike you as a strong response?
Applying this to your situation, imagine asking a candidate with a low LSAT score and GPA how they felt about their academic and testing performance. As you'd guess, I don't think "Yeah, I'm really sorry.. I just don't know what happened.. I was really disappointed.." comes off as too attractive. Nor does "yeah so, in my Econ class, my grandma died like the week before. And in my English class, the one where I got a B-, my professor was like 100 years old and none of us knew what was going on. And there was this guy sitting next to me during the LSAT who kept farting..." Even if all of that crap is true. And my guess is that something like "undergraduate grades and LSAT don't matter--I know I'm going to be an amazing law school student" comes off as presumptuous and stupid. At least for me, an attractive answer would be something that hit on points like (1) I genuinely applied myself in my classes and on the lsat, (2) I tried to learn from my mistakes by talking with professors and taking other steps toward improvement, and (3) I look forward to the opportunity to try my best in law school. And, of course, it would need to be delivered in a sincere and human manner where I actually believed what they were saying and didn't think they were trying to remember what their overbearing dad wrote on flash cards for them or something.
Anyway, the strong point of the thought experiment is just that it's a reminder that an interviewer is just another person. It's just you or one of your classmates in a few years. I think it helps to keep that in mind.
GL in your job hunting. And remember that the only thing great about biglaw is the pay check. (Even then, given the hours, it's questionable.) Being sunk in
law school culture makes you think that it's also the one-and-only key to happiness and self-respect, but it's not, and it's best to get over that mentality.