This exchange just popped back into my head for some reason. Your description of the approach to the flower was spot-on! Turns out it just happens to be a similar approach to Siofra. Took me a few attempts, and fire damage is a bit of a miserable situation for my dex build with a bit of int (level 150, scadutree... 9, I think? Maybe 10?), but I got there. I found that the best thing I could do was actually just to absolutely max out my own durability and accept that I was only getting one attack off per opportunity. I was having a really rough time avoiding the thorn eruption attacks, so the crimson seed talisman basically giving me two extra flasks worth of health was great. So long as I used fire damage and hit it in the "face" I didn't really need to do anything else to get plenty of damage

I have since gone through the specimen storehouse and found my way into Rauh, which I was absolutely delighted by because it looks exactly like Shadow of the Colossus and I'd been itching to get there ever since I found that waygate that gives you a preview of it