Excellent. Well done you and Whippet.
That and raw chicken wings are all my whippet will eat. She looks at me with disdain if I try to feed her anything else, no matter how tasty it is, even sardines are met with suspicion, horse shit otoh... 
We've taken on an elderly, bereaved dog before and the early days are not easy, but if you stick with it does get easier.
The first day my had the 'old gent' as we call him, he rang me and demanded I take him for a walk because he couldn't cope with constant howling and escape attempts. This carried on for a week 
We tried rescue remedy and later took him to the vet who prescribed diazapan, nothing stopped the howling. They're now inseperable and my dad would not be without him.
Give it some time and see how things pan out. I know you don't like whippets, nor did I, or greyhounds 
I believed they were ugly, scrawny, weak dogs, but once you get to know them you see past that, I now cannot believe I ever thought they were weedy, they are one of the most majestic dogs you can own and are mainly muscle once they're fit.
There are plenty of people on here who work with sighthound rescues, myself included, who will help you source a rescue space if it comes to that, but for now aty least stick at it and see how you feel in a few weeks. It's obviously a stressful time for you.
I'm sorry about your mum and wish, you her and whippy well x Make sure you take time to take of yourself.