I'm so sorry that you have lost your sister. There are many things that you can do to honor or do in memory of your sister. Here are a few ideas:
Plant a tree and have a stone made in memory of her to place at the foot of the tree.
Start a scholarship in her memory.
Donate to charities in her name.
Donate a bench to a local park with her name on it.
Donate a statue or other needed item to the church.
Ask your pastor if you belong to a church if you could start a rose garden or some other flower garden and let people put the names of their loved ones near it if they donate plants.
If she was employed, maybe you could ask her employer if you could have a plaque made to display in the building where she worked.
Give out memory cards to friends and family with her picture on it and maybe some personal information or a beautiful poem or prayer.
Make a website for her.... See the link below that a friend did for my daughter. Please sign the guestbook if you like.
Have a memorial service for her a year after her death.
You could bury in your yard some of her very personal things like clothing or shoes that no one else could wear. Put a memorial stone on top.
My mind is starting to go blank now. I hope that you can come up with something that will give you comfort. I know that that is so important when you are grieving.
Let us know what you decide to do.
Lu

Here is a link that might be useful: Christin Cosby Memorial Web Site

Yes, do let us know. Some of the things that we have done to honor and remember our son and granddaughter: we have donated to his high school and her school. Every year on Millie's birthday, I send books to her school library. We donated to the local zoo, which they both loved, and "adopted" a turtle for a year. Dave loved baseball, and Millie had been to several games with us, so we purchased a brick in their memory when the new Reds stadium was built. My friends at my school bought a bench and a tree in their honor, with a plaque dedicated to their memory. I leave the building that way each day, and I'm heartened to see their names. It's very important for us to keep doing this, as we attended their funerals, but they were cremated and when their ashes were scattered at Lake Michigan, we were not allowed to be there.