Hard to tell without knowing more about her and her condition/history/shaping-up habits. She obviously (to me) has had foals before.
If I had to guess I would say *at least* 30 days based on the udder photo. Going by her progress so far and figuring she has had a few babies, I would expect her udder to fill enough that the halves became seperated more (teats farther apart) and the teats to fill and become big and smooth and cone shaped.
Just to compare-- here is an udder with full teats. This mare started making a bag at almost 60 days out, and it built very gradually with some expected fluctuations. This mare went a few more days after the below photo was taken before she waxed-- she waxed a bit one night, alot the next morning, started dripping milk that night, the next morning she foaled.
The croup photo definitely shows lack of muscle tone/condition-- but has she lost tone recently, or was she already thin/lacking muscle when you got her?
Vulva shot-- doesn't look particularly ready... however I know with a few of my mares, they can look slack enough that the foal is going to fall out, but the minute you try to photograph "under there" they pucker everything right up.
All that said, mares can bag up huge almost overnight-- and of course there is no rule that says that all mares will be fully bagged up before they foal-- some mares foal with almost nothing, and get a huge full udder in the 30 minutes it takes the foal to stand up and start looking for it.