It is not too easy to tell from your pictures, but one of the things I see is that she has lost 'weight' over her tail head, which could be a sign of her being fairly close to foaling or it could be the result of your trying to slim her down. Not too sure where you live, but going into the winter months on a slim down programme is not the best thing particularly with an older mare.
If it is true or possible that the people who owned her before March had her running with a stallion (for how long????) then it is perfectly possible that she could be close to foaling any time from now on. But you really need to find out as you will need to adjust her food accordingly - not sure what she is getting at the moment.
Yes it is possible to feel the foal move, as stated above, when a mare is eating and also immediately after she has had a drink, but if she is far along in pregnancy, then the foal may be too 'big' to have the space for much movement. Have you seen any increase in her udder size as this will give you an indication as to how near foaling she might be - if in foal. Could you get hold of the Wee Foal testing strips? Or for a bit of fun you could try the ring test - you are supposed to use a Wedding ring but frankly anything metal will do, even a nail, and tie it to a light piece of string approx 12" in lengh, then hold it suspended over the mare's back just level/in front of her hips (make sure there isn't a wind blowing!) and watch for the ring/nail to start moving - be patient! A circular movement means a filly foal and a straight line - along the mare's spine - means a colt. No movement means no foal! Only a bit of fun and not to be counted on, but it has always worked for me.
But seriously, you do need to find out for sure whether she is in foal or not as it seems possible that she could be further along in her pregnancy than first thought and therefore you will need to get a mare and foal feeding programme sorted for her as soon as possible.
Good luck!