Is there something wrong with my cat?

i have got two 1 year old female tabby cats (sisters) they get on great with each other but recently one of my cats just started meowing and biting the other cats neck not aggressively like if they were fighting but more like nips and wen the other runs away and hides and she cant find her she starts to howl like it she is in heat but they havnt been spayed yet, could she be in heat if so this isnt how she normaly acts wen shes in heat