Hi Liz,
It's such a worry I know, I can fully sympathise. My mum ate and drank a similar amount to your Mum for 3 or 4 weeks during a urine infection, a week in hospital being rehydrated by drip, and the subsequent couple of weeks back at her nursing home. She is now beginning to take some pureed food, and I saw her eat 2 small mouthfuls of sponge cake the other day and nearly cried! It's amazing how grateful we can be for small mercies. She still has days when she is so tired and weak that she does the clamped mouth thing you described, but usually does better the following day. I know the nursing home you're moving her to is a new environment for your Mum, but hopefully it will feel less stressful than hospital for her. My Mum was totally stressed out by hospital, and visibly relaxed as soon as she got back to the home even though she is quite far down the line and not able to verbalise how she felt- in fact, the nurses sat us both on the bed, wrapped Mum in a blanket and brought us tea- hot for me, warm and sweet for Mum- and she drank it all down! I wish you and your Mum and family all the very best,
Alison