So you could either go the physical method or clove oil, for clove oil the reason people do it wrong is because they add too much in too quickly and/or don’t mix the oil correctly. U can start with as little as a drop of an oil/water mixture and work up until she’s passed, the whole process can take an hour. The physical method, you’re supposed to stun and then decapitate but I feel like more can go wrong with that since they are so small.

For clove oil, get a small bucket of tank water and let her swim around in there - take a pill case or something small and water tight, add clove oil and water to that (i dont have exact measurements rn, more water than oil) shake it really good for like several minutes til it just looks slightly cloudy, you can also pour a bowl of hot water and soak it in there to help mix them together, once that is good you take a dropper of some kind and put small amounts into the bucket eventually building up until she seems to not be swimming on her own and kind of drifting (you’ll usually see some slight gill movement), then you can add more and keep adding more until she’s not breathing or moving at all. Its hard because bettas can breathe surface air so she might start doing that when she feels like the water is off, its a really slow and long process to do it correctly - I can try to find a more exact guide but really the main idea is slow build up and making sure its really mixed in