Noone can tell you if she's ready. Cattle can "look" ready for a week or so. And, cattle normally eat VERY LITTLE 12-24 hours prior to calving. Going "off" feed is a good INDICATION that she's close.
She may have clear discharge for a month prior to calving. But, when it is long stingy discharge, that USUALLY is the start of stage 1.
Yes, the mooing CAN mean she's getting close. Some cows will start "humming" to their babies before going into labor, some during labor, others never.
When she actually starts stage 1, she USUALLY will want to be away from the rest of the herd. She will be restless, getting up & down, licking her sides, kicking her feet, or shuffling her feet - shifting her weight from one leg to other, swinging her tail. In other words, she will look "uncomfortable". This can go on for a few hours, than stage 2 should start with the calf entering the birth canal. The first thing that will show is the water sac, which is white in appearance. Sometimes it breaks quickly, other times it doesn't break at all till calf is out. Length of time for actual birthing varies greatly - and also depends on how often she is DISTURBED by the expectant owner.
Well tonight she was mooing an humming and walked away from the other two. She ate an enormous amount of Hi Mag minerals that I put out for her. She has been mooing and humming for about a week now. Tonight she looks very big compared to my bull, who is not fully grown, and my other heiffer. I am just concerned that she will need help and I will not be there. Your last statement, disturbed by the expectant owner, do you think we should just let her be and not bother at all or should we be on alert? That is my concern. Many people have told me she might need help and I do not want to shrug my responsibility. I really want it to be an easy delivery for her.
Hope this helps.