It's great your heifer is coming due and I understand the anxiety of when will the calf come. I have a close up old pet cow living in my front yard now so I can watch over her, even getting up at night to look with a flashlight. Dairy cows are not like beef cows. Generally, lactating Jerseys do not do well on all 'grass fed' diets. They lose so much weight they look like walking death and do not breed back. Generally, Jerseys are fed 3 lbs of 16% protein dairy feed per gallon of milk produced each day. You have to gradually increase the amount of feed that is required according to their milk output. Dairy feeds are already formulated so you don't have to worry about adding this and that.
If you 'share milk' and I do not advise it because cows and calves dont reaaly want to share. Cows hold up their milk and cream for the calf and what you get is mostly skim. And you don't know what her milk production actually is in order to feed her the right amount of grain. In addition, dairy cows produce so much milk the baby calves are overfed and get scours (diarrhea). Aggressive nursers, usually bull calves, cut up the cow's teats. If you take away the calf after she licks it off and bottle raise it out of her sight they quickly forget and there is no calf sharing drama. If you hand milk please wear disposable gloves and do not wash with water. I use an iodine teat dip leave it on for 60 seconds then wipe it off with clean cloth, using a clean spot for each teat and dip again after milking. So the dip is on the teat while the oriface is still open after milking. Cows get mastitis, the worst is staph aureus that lives on the skin of people's hands and can ruin a cow because it never really goes away. There are other mastitis pathogens best avoided. I have an old timey Surge belly pail machine and I love it. Still, I never touch her teats with my bare hands.
I milke a first calf heifer. You don't know what first calf heifers are going to do. They might not allow themselves to be touched or milked or kick off the calf. It's best to have some good quality powdered colostrum on hand you can mix and feed in a bottle. Because the calf has got to get colostrum in the first hour or 2 of birth or they have no immunity. Get the good stuff. its more expensive but it's made with cow colostrum protein. Avoid products containing soy and these cheap 'all species' colostrums. It's better to have and not need than need and not have. It's a good thing I had colostrum because my nice mannered heifer after calving she went nuts.
Also, I would advise putting out purina Wind and Rain high mag (magnesium) loose mineral along with a salt lick. Cows can get grass tetany when the green grass comes in.