Possible Ideas for you
First off my prayers and love to you and your sister. I have some possible ideas for you to look at. I made the first one the Angel with ribbon and leaves for my future-sister-in-law on an apron, I'll attach a picture for you to see how it turned out.
Another angel idea and maybe a flower bud in a heart templates. I personally would make different blocks with vibrant happy colors and designs, but that's just me.
Hope this gives you some ideas. Let me know if I can help in any way. Good luck. Please share the final outcome.
Again, prayers and get well soons for your sister.