I feel like you are not thinking this through. As a child, Cassandra must have thought that Mother Gothel wanted another child. If I were Cassandra, I would have thought: my mother hates me, she wants another daughter, and now she has left me.
And heck, Cassandra is pretty much right. Mother Gothel treated Rapunzel much better than her own daughter.
I wouldn't be surprised if that was one of the thoughts running through Cassandra's mind during that moment. She spent her time doing whatever her mother wanted her to do in the hopes of gaining some love and affection. She never really received that and instead was replaced with a different child, so that would make her think that she wasn't good enough or didn't do enough to earn that affection from her mother. This is a big reason why I don't want that memory to be fake. It ties in nicely with Cassandra's desire for having her own moment to shine and provides a good emotional unconscious reason as to why just waiting for that moment has been hurting her for so long.
Although, I don't think Mother Gothel treated Rapunzel much better than her own daughter. She did lock Rapunzel away for eighteen years just to keep herself young. She effectively treated her more like an object than a person because that's basically what Rapunzel was to Gothel. She was the new sunflower that she could use to restore her youth and beauty. Plus, she was still pretty emotionally abusive not only with isolating Rapunzel, but also with tearing her self-esteem down enough to where she'd question if she could handle the real world. Even the whole "Great, now I'm the bad guy" line can be read as an emotional abuse tactic to make a person question if they're in the wrong for just being upset or sad. I think that Gothel used two different kind of emotional abuse methods with Cassandra and Rapunzel. She kept Cassandra at an emotional distance to where she'd want to do what she was told in the hopes of being loved. She was a bit closer with Rapunzel, yet still emotionally and physically distant, in order to make her stay in the tower.
Anyway, I thought that today's episode was pretty good. I wasn't expecting Red and Angry to get new designs. It did make me wonder how much time had passed since they ran into them during season two, but kids have growth spurts all the time. I'm also still really confused about where Rapunzel's parents are. I don't think that they've been seen or mentioned since the season premiere and I'm not sure if their memories were restored. The art style used to explain the curse of the werewolf was so cool and really helped to give off a Halloween kind of vibe to the episode. I also kind of liked how no one had the typical disbelief reaction to the werewolf myth. Granted, it would be kind of weird for the characters to question it after everything they've gone through, but I was almost expecting that to happen. The concept of werewolves existing in this world was also pretty easy for me to believe, especially when it is such a well established myth in general. That nightmare sequence was pretty creepy and I almost thought it was real until everyone turned into a werewolf.
Monty seemed like a weird red herring, especially when a paint leaving a paw mark liked right on his neck just seemed so improbable, but I kind of liked that Rapunzel wasn't upset over ruining her chances of a resolution between her and Monty. Red being the werewolf wasn't too much of a shock, but I kind of expected both of them to be the monster. I thought that Rapunzel chasing after the werewolf hinted that there were two of them, but Red being that fast made more sense.
The situation between Red and Angry was a strong parallel to Rapunzel and Cassandra's current relationship. I don't think that Rapunzel was bossy or dismissive of Cassandra's feelings, but she was still unaware of Cassandra's feelings. Red being upset at everyone assuming that she's okay just because she doesn't say anything was way too relatable. I don't think I was non-verbal before like she has been in the past, but I can understand the struggles of being too shy or uncomfortable to express myself. The werewolf hunter was pretty cold. She had no problem with killing a child. Sure, she justified it by saying that she was a monster now, but she was still effectively trying to murder a child. Maybe it wouldn't be as morally bad if Red actually did hurt someone, but the most she had done was just scare livestock around Corona.
I really liked how the resolution was handled. Instead of calling each other by their nicknames, Kiera and Catalina were more open and honest with each other. Kiera apologized for ignoring Catalina's feelings and promised to do better. Rapunzel pointing out that it's okay to be angry and upset, but that Catalina was just going about it in an unhealthy way was also really good. They had a good compromise with making a more fancy treehouse close by. Like Eugene pointed out, it wasn't exactly living in the wild or in civilization, but a good middle ground for them to compromise. That's a really good message in general as well since they were only able to find a solution by communicating with each other. Catalina still being a werewolf was an interesting twist. Since they live close by, I wonder if she and Kiera will show up later to help with Cassandra. Rapunzel seeing that picture of her with Cassandra after saying that burying one's anger doesn't help anyone was pretty sad timing.
Cassandra having to embrace her rage and hatred was a dark mirror to what happen with Catalina. Instead of dealing with those feelings so that she could happier, Cassandra is being encouraged to be overwhelmed by her own feelings in order to master the Moon Stone. It also explains why she was able to use the Moon Stone right away, but struggled afterwards. Facing Rapunzel and explaining her past would make all of her hatred, rage and pain feel so fresh and make it easier for Cassandra to use the Moon Stone for herself. Overall, it was a pretty good episode.