First off, we are very sorry to hear about the loss of your grandmother. Our thoughts are with you and your family.
Not to worry, it will be just like any funeral with a casket. The only difference will be if she is cremated before the service, they will just have the urn of ashes (completely closed and sealed) up at the front of the church instead of the casket. If she is to be cremated after the service, she will probably be there in the casket and then the cremation will be done by the funeral home after everyone leaves. Unless something extraordinary has been requested by the decedant, the family and friends are not around when the actual cremation takes place.
After the cremation, depending on your grandmother’s wishes, the urn will either be given to her family, or it may be placed in a columbarium or similar memorial facility if she is to be “buried.”
I was 21 when my father died, after a very long bout with cancer. He had asked that his body be donated for medical research, which was done. We received his remains back from the medical school about a year after his death, and had them cremated.
We had held the funeral/memorial service right after his death, but did not have a “burial.” A year later, the major emotional shocks had worn off. My family was all pretty matter-of-fact about having a very small, quiet ceremony to place his ashes at Arlington National Cemetary. We had focused on his “life celebration” at the memorial service, and placing his ashes was a smaller event for us.
In the mean time, I had taken a new job, and my boss didn’t know that my father had died a full year before. I walked into his office one morning, and said “can I take the afternoon off? I need to bury my dad. I just need a few hours.” He naturally thought that it had just happened. The look on his face was priceless - he couldn’t tell if I was the most callous son in the world, or just completely nuts. I thought for a while about just leaving him confused (he was already convinced I was not entirely normal), but finally relented and let him in on the story.
The bottom line is: it will be a normal memorial service. They are frequently very difficult to get through, because of the emotional loss. But there is nothing to fear about her desire to be cremated, it will not add anything unusual or traumatic to the service.