If anyone plans on doing Broodmother on Hard mode and you haven't done her before, please do yourself a favor and practice on medium first and make sure you can get her stuck consistently so that she doesn't attack you, I don't want anyone to lose their rexes because they were ill-prepared.. You can even practice on easy if you want to save the tribute resources. If you do not get her stuck she will demolish you and your rexes before you have a chance to kill her no matter what HP or Armor you have on your saddles, that being said however I still encourage to NOT skimp on a decent hp pool or a good Saddle BP.
We did Broodmother on Hard tonight and it actually went pretty well, but only because we got her stuck. We took in 3 players/20 rexes and of those rexes, the stats that 80% of the rexes we were running were 25k HP and a little bit above 700% melee. (See first Screenshot)
When we went in and started moving our rexes into position a couple of them got stuck momentarily while they ran into one of the pillars, because Dino AI isn't the smartest AI. One of the rexes in particular "Zella" Took a few hits before we got into positioned and before we got the boss pinned. Zella lost 19k of her 25k HP after the fight was over with a 86.4 armor saddle and even the other rexes took 3-5k damage even though we had her pinned for 95% of the fight. In the 2nd and 3rd screenshots below you can see Zella and the damage she has taken via the blood marks. In the 4th screenshot is a picture of Zella's stats several hours later(taken for this post that I decided to make later). Also a testament to not mess around with the baby spiders, one of our rexes (Helsa) took a dive off the bridge and died in about 30 seconds or so just to the Araneos alone, that being said the spiders are only able to be summoned if the Broodmother is not pinned. The 5th screenshot is Broodmother's stats postmortem if anyone was curious.
Some Final Notes : Until there is a rebalance on the bosses(if ever) I do not think it is physically possible to kill Broodmother with out pinning her, if you do not pin her she is demolish your rexes before you have the chance to dish out enough damage. There is a fair bit of improvement we could do and want to do for our rexes but in a 1v20 head-to-head match I do not believe the rexes would win, even with the improvements such as 45+ base HP stat, 100% imprint, or a higher armor rex saddle. If I left any important details I include them in an edit or if anyone has any questions feel free to post here. Also as a shameless plug, if anyone is selling 45+ rex stats that are unmutated/wild tame I'm very much interested in buying anything except for melee.