I'm including a link over to Luna's mare's thread on this forum:
https://www.miniaturehorsetalk.com/threads/pregnant-mini-mare-advice.139632/page-3#post-1643622
The reason I did so is that your mare has a similar body type. I also seem to see more filling in the teats themselves, compared to the first photos you posted.
Could you check her lady parts? Are they more elongated and/or puffy? What color is the inside when you gently spread the lips and check? Light salmon or darker? Is her tail loose or can she still clamp it down?
In the interests of covering all bases in this crazy weather, have you checked her gums? Are they moist and pink, or dry-ish and pale? If you press them with your thumb, does the white print return to pink quickly? (Capillary refill time.) If you pinch the skin on her neck into a tent, does it drop flat quickly when released or is it slow? (Dehydrated.) If she'll let you listen to her sides, do you hear plenty of loud gurgles and plinks? If this all seems normal, her temperature is normal, and she's just not her normal self, watch closely.
Since she WAS in with a stallion, keep your foal kit close at hand and your awareness up.
Brisk hand walks and light trotting won't hurt her, so feel free to start light conditioning. Even if she is in foal, the exercise will do her good. Just be sure not to work her until she's sweating or starting to breath hard. In hand obstacle work is good, too. Over poles work helps build muscles, as well as trust when you two walk over them together.
If you're concerned about colic, you could soak her feed until it's like very thick oatmeal. This will get extra water into her. You can also add Gatorade to her water to encourage her to drink more.
If she's rubbing, remember to check her udder for crud, too. Itchy ****ies make mares do all kinds of strange contortions.