Either get a halter on her and "tie her"to a post or something, or get her used to putting her head into a head catch of some sort, like a stanchion, so that she can't move away from you when you touch her. And don't get her all upset, but just to get her to realize that you touching her isn't the end of the world for a few days/week. Then she will eventually not even flinch when you touch her. The big thing is to make it so she can't move any distance away from you and to touch her then to just take your hand off of her a few times until she isn't so skittish about it. Some get used to it quick, and I have one that still isn't too keen on it after her 2nd calf, but she will tolerate it enough to let me milk her. She has become a nurse cow and I can get 2 more calves on her plus hers, and does a fine job. She just isn't one for touching. Have another that would probably let you lay on her back, she is so tame. Sometimes a brushing will be more accepted at first as touching sometimes seems to be too soft for them and a brushing is firmer and they don't want to " swat it " away..
Get a 2nd calf as soon as possible after calving so they are like twins to her. If you are graining her for the milking process, I don't think you will have to worry about her not having enough milk for both calves plus the house. You will get a routine going with her and find out what works for you. I would separate her calf from her like overnight, then put the 2 calves on her so that she can smell her calf and not pay as much attention to the newer one. Keep her in the head catch or stanchion, so that she can't turn around and butt the new on and after a couple of days, the calf will smell "right" to her once the milk gets into it's system. Cows associate by smell, ever notice that they will smell the rear ends to check them out? The cow is able to determine "her calf" by the smell of the manure from the cows own milk going through its system. That is why I push getting a cows milk into the calf for at least one or two feedings before letting the calf actually suck the cow if it is possible. But again every cow is a little different. A little urine from the cow and a little manure put on the calf makes the cow smell it and it smells more like "hers" . If you are real lucky and get the afterbirth and rub it all over a new (extra) calf, will help too. But the milk going in will make the manure coming out the other end smell right to the cow.
Lost an old cow about a week ago, not sure why but the heat probably didn't help. The calf was about a month old and had 2 younger cows freshen about the time the cow died. That month old calf has taken to one of the cows, and she is allowing it to nurse right along with her calf so we will let her raise them both as "twins". It is her 2nd calf and should have enough milk to do an adequate job. Was glad that the calf was hungry enough to try to steal, and a bit surprised that this particular cow would allow it, but she stands like an old milk cow and they both go right on her. Her half sister that calved at the same time, seems to be tolerating the calf as I did catch it on her once with her calf also. So between the 2 they should be able to raise the 3 calves. Usually we aren't that lucky.