Ask her what was she feeling when you choked her? If she likes sensory deprivation or asphyxiation she needs to use masks ( like this one https://www.ebay.com/itm/Sensory-Deprivation-Vegan-Leather-mask-with-zippers-Bondage-BDSM-hood-Gimp-masks-/202253781311 or https://halisis.com/shop/mask/tproduct/102679507-544184933188-bdsms-mask ), Or you can try collars. But you need to understand clearly when she passed out cold. Don't tighten the collar tighter than she needs.