When my oldest cat died, I put her on a blanket and let the other 2 cats sniff and look at her. It was like a little funeral. I did this because I read somewhere it was good for the surviving cats. I don't know that it helped or not. I do believe pets grieve.
I'm sorry for your loss and my thoughts and prayers are with you.
Dove
Cats (and dogs, too) absolutely do grieve for their lost friends. It takes them a few weeks, usually, although in some cases it can take longer, but they eventually come to grips with the idea that their friend is no longer there. You can help them through this period by giving them more attention and making them feel special. Maybe give them more one on one playtime than you have in the past, some new toys, some special treats (find a recipe online for liver brownies and bake them a batch). Eventually they will get used to the new order of things and will settle in to the new situation.
Ghilly
The great thing about animals is they are capable to adjusting to loss, if you give them a fairly stress free, stable environment. Just be patient, she'll adjust. Cats are usually pretty good at coping with death. I won't say she'll forget in a few weeks...but she will put it in perspective.