Although this is not exactly the "right way" to describe it, for practical purposes it is easier to understand. A cow that is making milk and letting it down is something like milk in a jar... the cream "rises" to the top... so the greatest concentration of butterfat is towards the end of the milking.... "top of the udder" so last to come down. That is where people say the cow is holding up the cream... well actually she is not holding the cream, it is just that there is more cream towards the end of the milking session. When I do the milk testing, I have to make sure I agitate the milk in the meter so the butterfat is mixed in so the milk I draw out the bottom of the meter, is not all "skim milk"...
Size of udder does not necessarily have much to do with actual production. It does allow for more capacity, but that doesn't mean the cow will milk better than a smaller uddered animal. My longhorn has what I call a "tea cup" udder and it has got to be very high butterfat because she raises FAT, butterball calves... and for the first 2 calves you couldn't even see the udder.....
There are several young cows on a dairy I just tested with them making 35-45 lbs milk at one milking and you look at them and wonder where they hid all that milk in that "tiny udder"... and some older cows that have large udders that make a huge amount of milk..... The thing is you want the udder to have good "attachment" so that is is not hanging down like a basketball in a small bag.... you want good fore udder attachment and good center ligament attachment in the back with good definition between the 2 back quarters...
I am not in love with the udder on the cow you pictured, but it certainly is not the worst I have seen... getting her milked out and taking out some of the pressure, and the edema, will go along ways.
Because of that, she would have a short life in a commercial beef herd, but there are worse things... hopefully, the calf will get it figured out and start to suck.... and then will help break up the edema by butting her. She is a nice animal overall....
Suggestion... get some of the "udder spray" for dairy animals... it is a mint extract.... usually always a blue spray... the mint causes some heat and the heat causes the edema to break up better... helps with hard tight udders also... and will get more blood flow to the area which will also help to prevent mastitis..... they make a cream also to rub on the udder and some like that... would make you think of "Vicks Vapo Rub" except it smells minty... but creates some heat and it really does help with blood flow which helps with edema and such....