Schoolnurse, I am so sorry you are going through this. You are having a very hard time.
Firstly, it's natural for dogs to lose their appetite a bit when they are stressed out (like whippy obviously is at the moment). It's also very natural for them to eat less when the weather is very hot as it is at the moment. You've also previously said that this whippet is very elderly and is used to a routine of little treats all day from your elderly DM.
Putting all these factors together, I'd say it's completely understandable that she is not eating much at the moment. Many elderly dogs have poor appetites and can't cope with one or two big meals a day. If I was fostering her, I'd be presenting her with very small, tasty snack meals three or even four times a day. Just little plates that she can finish and enjoy. Nature Diet is available from Pets at Home.
The other thing I'd suggest is a very small tin of sardines or my other go-to for an elderly prima donna is to buy a cheap packet of frozen chicken breast fillets and bung them in the slow cooker with some water. Cooked and cooled, they can be shredded, with a little dry biscuit, and the broth dribbled over to soften the biscuits and smell appetising.
I honestly don't think this is "pandering"
- elderly dogs (like elderly people) undergo physiological changes as they age, and in addition she has built up a routine for feeding with your DM that she was used to. While she's with you, I think feeding separately is an excellent idea, with the understanding you are currently working on a longer term solution for her. If you are finding it too difficult and stressful to cope with her needs at the moment, which would be very understandable, please, please do contact Cinnamon Trust and discuss with them an emergency foster placement - the current situation is sounding very stressful for all of you.
Wishing you all the best, and so sorry again you are going through this.