Holy rump roast!!! You don't see that on Angus cattle. Not being familiar with your breed, clearly, I can't judge by the pic. But as a general rule, when they're close to calving you should see the mucus plug, the aforementioned tail raising/sideways, quite often pacing, up/down a lot, if they're not contained they'll leave the herd to find someplace "private", the pins by the tail will get soft. Some heifers bag up a good couple days before calving but sometimes there just isn't much of a bag & they don't come into milk until after they've calved.
Just keep an eye on her.