Hi and welcome! If you need a quilt that can stand up to lots of washing, I would stick to cotton fabrics. Mixing cottons and silks is a great way to create a quilt with texture but silk won't stand up to constant washing. Perhaps velveteen (cotton velvet) if you want different textures in the quilt surface would be an option instead of silk?
Perhaps using your sister's favorite colors is a start.
If you have a picture of something she created you can recreate it with fabric.
Another option is to create sections of the quilt utilizing your childhood memories of fun activities. There is nothing more individual than personal memories.
You can add embroidery to sections of the overall design to represent the singular memories to personalize the quilt.
Don't underestimate the power of words in a quilt. Use words that describe your sister.
As far as patterns go, I would suggest googling "modern quilt patterns" and see if anything sings out to you. You can add elements to the pattern that give you the personalization you want.
You can google "paper piecing pattern ______" with the blank being whatever the unique item to match your sister could be. There are tons of very creative paper piecing designers out there that may have a great pattern for you to consider.
I am looking forward to seeing the quilt you come up with!! I am sure your sister will love it.