Wow, I guess she really was heavily enamoured with Shien-san, but there's not much trauma so far...
No worries though. During last time with Mode-chan, we also get to see her cute side only on the first half of a chapter, and the trauma came later.
I see now that she really is the Tama-Shien duo's powerful sponsor, giving them gold so that they're able to provide medicine for the people for free.
I mean, I believe it's not really as bad as they led us to believe. Unlike Mode-chan who loves her animals and Tama, her biggest fascination is Shien-san here first and foremost, so I'm guessing that her loss of memory was a personal decision because she wanted to protect her beloved witch. Or (more likely), she heard about the hunt first from common people, and afraid that Shien-san was caught or wasn't able to get money to live anymore, so she tried to make money and go to the war zone (for witches, it's burning stakes) and got captured with gold and got suspected, or maybe she saw Shien at her worst, tried her best to save her, barely succeeded, and got in a devastating place herself.
After all, she doesn't display much witch properties, so her possibilities of being taken out during the hunt is rather low. If she really was caught in the witch hunt, Shien has to be the primary reason. Not to mention I believe Shien-san was the only one who is able to erase memories with witch magic. (Rea is only Alchemy, right?)
Who knows, maybe she also has something to do with her like towards cigarettes (albeit used cigarette butts) before cigarette were even invented. During the Hologram Tama Recruitment, she was the only one who smokes among three vegabond witches, the other two being Mode-chan who is just a dependent child at heart, and one final witch who uses a lolipop.
I also hope that Rea's tale can have more than one chapter, though. I somehow think that her journey needed more than a single chapter to cover. Her desperation feels like it would be better told in more detail to the memory-loss Breaking Point. But can the manga justify a trauma event so bad it warrents an empty head in half a chapter? Or give an accident memory-loss that feels not so forced? Let's wait and see.
Also, Happy April Fools! hehe, who would know that a simple fool moment could have been a fact check on black tea? You really got me there~