A very young snake is eating very young rodents, right? Well, they're very digestible- they don't result in a lot of waste that a snake needs to expel, & in an effort to also conserve water, snakes just don't defecate until they actually need to.
It may take a month or more, but you can actually HARM your snake doing as you did- not so much the bath (that "just" causes stress, which in turn may cause refusal to feed), but "manually manipulating" a snake's body could injure them or interfere with needed digestion. Please do NOT do this.
Actually "her brother...which has gone 3 times in the same time period" is actually the more unusual one, & might have an issue. It's uncommon for snakes to get constipated- & if they do, you'll generally see what we call "sausage butt"- ie. some amount of puffy swelling above their cloaca, & you may or may not feel some hard lumps (feel VERY gently please so you don't cause a rupture!)- the hard lumps may need help to pass (urates sometimes form these "stones") but getting professional help from a vet would be ideal, if a little soak or swim in shallow water & normal routine handling doesn't inspire your snake to relive itself. Okay?