The Pink Hag (who is named Shakaeda for those who care) is a Gwyllion, a new hag that I created. I have the information in this HTML file that people can use for their own campaigns if they want an alternative to the hags already available in the Monster Manual.
Your Hag nearly got TPK with a one shot interim game that I ran. Some very lucky/unlucky rolls on both sides the screen. Anyway, what did you use to create the sheet for the creature?
The Gwyllion functions more as a spellcaster type enemy than a surprisingly beefy combatant like the hags normally are. If the party gets initiative before it does, the outcome is quite often the same as if the party ganged up on a level 6 wizard 'standard race' enemy. Shakaeda (Gwyllion) only got a couple of decent magic spells in before got pretty effectively neutralized by Dalania (Annis) via grappling.
The sheet was generated via eTools, probably one of the best Dungeons and Dragons tools there is out there. I also developed the monster through the program, though I did some guesswork on the CR and the abilities to make the CR appropriate. If you wish to make any other Gwyllions more challenging, you might want to roll the stats to beef them up a bit. I usually do this with my monsters whenever I pit them against player characters. In terms of advancing the monster, since the Gwyllion has spells as a level 6 wizard, the wizard class is considered associated, so caster levels from the class stack with her spell levels.
The Gwyllion worked well as a roaming intelligent creature/amusing sidequest because it ended up with and using some of the PC's gear (they had a mishap with a metal teleportation rune) and the Players liked it despite it using their own equipment against them, especially the Wizard's Spellbook. A few of them might end up reading OLA because of it.