I'm sure your sisters really appreciate your letters. It's great to see you send them off so well!
One year we had 3 sisters graduating, which is a lot for us. I made sure to get little gifts for them...i believe it was a candle with a rose pin stuck in it, PSS engraved.
However, the chapter has no tradition with senior sister send offs...eg, i got nothing, not even a letter - but I knew my sisters loved me and appreciated my work.
I'm not sure if they did anything this year, i don't think any are graduating, just a few transferring away
Just remember soon you may see them at an Alum reunion!
LITP