that really shows her maturity level there. If i were in this situation i would just drive up to her house and get the mouse. (id love to add in some more details as to how id do it but they be deemed illegal and therfore banned by this site lol). I think they are joking around a bit bc this is "just a mouse to them". Thats BS imo. The attitude shes showing is almost like serial killer like tendencies lol. Stealing a living animal from someone, holding it hostage, then when they try and get it back joke about killing it. Thats pretty messed up if you ask me...
I would love nothing more than to teach her a lesson by giving her a dose of her own medicine.