Do you have any photos of her before she delivered? She does look pretty thin. BCS of maybe 1 1/2- 2? Hard to tell from the photos. Any idea of her age? Maybe she's a broken mouth cow?
Had a couple of dairy cross cows end up looking like that usually found they were feeding more than one calf I usually move them up into another paddock near the house drench and feed them up for a few weeks if they dont start to improve its time for the vet or the knackers
Good looking calf. I try to keep the cows condition up, but my purpose for the cows is for them to produce calves. So if they produce a good calf year after year then I keep them, no matter what they look like. If they look great and don't produce an annual calf then they are useless.
I have Murray Greys, too. When mine start dropping weight I make sure they have 2+ good flakes of grass hay morning and night; mine usually get grain as well, which helps a ton. Make sure she gets minerals (loose if possible) and that the other cows are letting her eat.
Some alfalfa pellets or hay will help her weight wise, and for milk production. Has she been dewormed recently? Parasites flare up at calving time.