Only one of her dark spells made it into the final cut, the one which had use in war against septarians. She used high mewman for it to avoid unwanted readers and locked it against her husband (who kept on peeking inside her chamber)
She didn't see what the problem was or why would anyone consider it forbiden, even Star felt it was a let down and nothing impressive or scary compared to the others... mainly because she only payed attention to the fun ones like the Allseeing Eye.
But, if you think about it, it's normal Glossaryck didn't want queens with Butterfly mode learn about a spell with can corrupt magic if you are in contact with the realm. He allowed it with Moon because it was the only one who could save the day, and also because she didn't know high mewman and would had to make a deal with Eclipsa, leading to her liberation.