IMO 5 months is too young to have free reign of the house, even when you are home. I would crate or confine her when you cannot directly supervise (night, when you are gone, etc.). When you are with her but not playing or training, keep her on a leash clipped to your belt. That limits her ability to sneak off. Also, make sure you teach her how to tell you she needs to go out. Some jingle bells on the door are easy. Just jingle them every time you open the door... you can work up to getting her to do it.
Was the poop this morning in her room or was she roaming free? If it was in her room, then go back to a crate.
Can you hear her from your bedroom if she needs to go out in the night? If not, consider a monitor so she can alert you.