do you guys know of any kind of bikes that can hold a second person in the rear rack? most of them only seem to hold 40 pounds, but she's like 10 and probably around 70. i really don't want to get a tandem since i ride alone the majority of the time, but just like a detachable cushion seat.

she's my niece and i offered to bike her to school in the morning, but i'm afraid she'll go too slow on her own bike (our narrow bike path is busy and crowded in the morning)

thank you