Thanks everyone. I spent a sleepless night and was out twice in the field in my dressing gown and wellies with a torch! It was a black, moonless night, but fortunately the rain seems to have stopped for the moment.
Anyway, this morning the news is good. Maisie is in the field grazing, and putting weight on all her feet. She will not let Tartine suckle yet though, and pushes or lightly kicks her away. I don't know if it is because it is time to stop her, or if she is feeling discomfort. Her teats seem normal - no signs of swelling or heat. Tartine is OK, she was only suckling a bit occasionally anyway and is eating and drinking well on her own now.
Now I have find someone who will hold her while I give her the next penicillin injection!
Keep the vibes coming - she is not well this morning and I have called for another vet visit. She hasn't eaten anything - does not even want any apple and was lying in the mud outside her shelter when I went to see them this morning. I led her into the shelter and she just immediately lay down again, at least on straw this time. Now she is standing outside, her head down, looking very dejected. She is not trembling though, the way she was on Saturday. I am scared not just for her, but for the foal she is carrying. I have to say I feel very helpless.