ok my theory
Peacemaker glows blue when some one who isn’t the heir uses it but knows it must work for whoever is using it as a necessity e.g when Wynonna pointed peacemaker at Willa - wynonna wasn’t the heir because Willa was alive however she wasn’t the true heir and was evil so peacemaker knew it had to shoot her and when waverly used peacemaker she wasn’t the heir but she had to shoot Rosita because she was threatening wynonna’s safety while giving birth to the next heir so it needed to work for waverly















