Charlotte, have you tried contacting by email, this may elicit faster response or contact Starlight Trust in Wallington direct, again by email!
Hope Maisie is right about it being just a bad sprain that will heal in time ... you are being of tremendous help by providing regular feed & water!
First time I've heard of Martins Heron, looked it up on Wiki!
2013 photos & vids here
eff37 on Flickr
Looks like good news, last night as it started going dark the jackdaw seemed to be getting really restless up in the tree and I saw it fly a short distance to the trees around the park at the back of our house. I checked this morning before I left for work and the jackdaw was definitely not there, however, when my fiance left he said it was back. It seems it can fly short distances and is coming back for food and water.
Great news looks like it should be OK, getting better whilst visiting your cafe for food & water! Good that you can still see it making progress!