Oh honey, you poor darling. Life can be so very cruel. Losing both parents by your age is terribly sad & unfair 😞 My Dad lost both his parents by the time he was 16, yeah life is so cruel sometimes.
My Mum is like my best friend too and we talk about anything & everything, I understand that bond & the pain when that is taken away from you. What a blessing your Mum knew your little girl and I'm sure will look over her & you forever. I'm really believe that.
You could keep your Mothers memory really alive for your daughter with photos and stories etc so that she grows up feeling like she really knew her Grandma?
I'm sorry your brother and you aren't able to get comfort from each other, that's difficult. Do you have a partner? Close friends? who you can lean on and talk to (apart from talking to us which of course you can always do!)?? I have a friend who lost his Mum to cancer and understands so well what I'm going through. Even perhaps a support group may be helpful for you?
If you're not ready to return to work, then don't (if you don't have to) ... and try and do something nice for YOU, sometimes just simple things can lift my spirits, like taking my pups to the beach and playing in the water with them and feeling invigorated by the salt air and water.
I also have an illness that is debilitating and I haven't had kids and I want to (when/if I meet the right guy) but I'm scared of how I would cope with a baby and this illness .... so I can empathise with that and now without your Mums physical support (because I'm sure she's still emotionally there with you!) ... is there anyone else who can help you?
Wish I could make you a nice hot chocolate, plop you on the couch with a warm blankie, your fave movie and some chocolate (((hugs)))