Why would the men think that Mina would be safer all alone in the vicinity of Count Dracula than hunting him with them? She's too delicate to break into Carfax to search for the boxes of dirt and to witness whatever they may see in Dracula's lair, but she's OK to be alone where they've all seen Dracula as a bat flying around looking into windows.
Maybe Stoker was an equal rights advocate who was pointing out how silly it was for them to consider Mina someone who needed to be protected from manual labor and manly pursuits such as vampire hunting. By excluding her from the good stuff and making her go to bed while they went out, they left her totally vulnerable and in a perfect position to be victimized by a vampire or anyone else, even one of the mental patients in Seward's care.
Mina's husband, Jonathan, doesn't even have a hint that something is amiss when he mention's Mina sleeping extremely late the following morning, being difficult to awaken and looking pale and weak. Her husband wasn't around to see Lucy's symptoms after becoming Dracula's victim, but everyone else was, including Mina. If I were Mina I would have noticed the bite marks as well.
Maybe they all just assumed she was having her time of the month!