She does not take a follower slot. She also wears her own custom vault suit.

UPDATE: Now there is a busty vault meat as well:


Extract the files in the Fallout 4 directory, so that the txt files are in the folder with Fallout4.exe and the esp is in the Data folder.

When in game, go to her at the Vault 111 entrance and click on her in console then type:

"bat vaultmeatfollow"   (be sure to spell it right)

NOTE: The busty version uses a different race and therefore most outfits won't show on her, to be able to dress her use the older version.

To make essential:

Type In console- 
help "vault meat" 0 (or whatever character you are trying to make essential)

then

setessential baseid 1 (baseid is the one you found with the help command)

To test:

click on them in console and Type:

kill


Credits to Aleanne for the Ruined Vault Suit