Why does my gf feel the minute she's tired she can just go to bed and leave Jace with me or my mom…

Why does my gf feel the minute she's tired she can just go to bed and leave Jace with me or my mom not even making sure he's cool? Once she's tired that's it, its bedtime regardless if the kids are taken care of. Me on the other hand I can't go to sleep without making sure everything is done for them and they are in bed