Stat Block for Lolth Vessel

Hi guys! I kinda need some help with my Big Bad. This whole campaign I have been hinting at the fact that Lolth is the puppetmaster of all the chaos happening. I want my group to have a big ol’ fight with Lolth but i feel like having a literal GOD might be too much. Instead one of my drow players has a drow NPC gf and they have been having visions and shit this entire game. The players background says he was able to leave as a baby and thus not as easily influenced by Lolth. But his NPC gf lived her whole life in Lolths realm. I was thinking of making the Gf an unwilling vessel for Lolth but I have no idea how to do stats (aka whats too op or what is a joke for my players levels). I have 4 players (3 level 5 and 1 level 6), a tiny pet lizard who isnt very smart and is very squishy, the NPC gf level 4 and a level 4 knight provided by the deck of many things. Due to the amount of actions they are able to make due to the NPC i tend to make their fights a harder just to keep them on their toes. (Plus one of my player is a Cleric here and he is VERY good at combat lol). I want to make this a challenging fight with high stakes. I would also like to do a willpower save for the Drow player since he would have to fight of lolths influence and also be willing to hurt the one he loves. If you guys could help me out or give me a general idea on how to do this stat block that would be amazing. I typically ask my fiance but he’s a player here and i dont wanna spoil it 😅 thank you guys ❤️