Look at Martin's other vids though
Not saying she had perfect form, but if you're not feeling pain during or after the lift, you've generally done okay. We train to be able to lift this way and Leesh's 122.5 vid was a tired third attempt that she hadn't succeeded at doing earlier in the week. Her form on lower weights is normally much tighter in the lower back, as is mine. If she has concern about it I'm happy to work with her to stamp it out and keep the form stricter, but I don't believe that anyone lifting their absolute maximum weight (as in struggling past the knees) will be able to avoid a bit of back rounding in the lumbar region. She has long levers and consequently keeping a neutral spine at max weight is much harder without it turning into squat.
A couple of interesting and scientific articles from people who don't believe it to be a bad thing, as long as you aren't reaching end flexion in the lumbar:
http://www.liftbigeatbig.com/2014/04/its-time-to-shut-up-about-rounded-back.html?m=1
http://www.t-nation.com/free_online_article/most_recent/a_strong_case_for_the_rounded_back_deadlift