I feel that the act of her callously cutting off her hair to punish you is what is really affecting your ability to maintain an erection, from what I've read you have tried many different things and are very willing to put in the effort to make things right again.

She had a lot of power over you with her long hair and she knew it, the fact that she punished you so severely for a minor argument will greatly damage your relationship on a subconscious level and will take time to recover.

Take your time, stop trying to force things too quickly, the more pressure you put on yourself to perform the more difficult it will be and you'll both be even more frustrated.

Be sure to be open about your feelings and how she made you feel, maybe you still have things you need to discuss.