Many PTAs or PTOs now do a teacher inventory and keep it on file somewhere in the school of the teacher's favorites. As a former teacher, I loved the keepers too, things that were themed from my university, a picture frame, a surprise Starbucks. Even bring her lunch one day, or send her home with a basket of dinner (maybe on a Friday and tell her earlier so she can plan ahead). Gift cards to get nails done are fun too. Some people in my area will do a lamp base painted from the whole class. There are some pottery places that do this, or you could have each kid do hand prints or thumbprints all over it to personalize the item. Another whole class idea would be to give her a stool that his painted or whimsical (or a chair) that she could use in the classroom. Maybe make a digital scrapbook for the end of the year if possible (I never made one for myself, but I would have loved having one for each year I taught!).
And ditto on the books, you can never have enough! And even just volunteering for her is very memorable. Go and read to the class, many kindergartens have some computer time where having extra hands is a huge blessing, and even others do a "cooking" time where it is great to have help. Change bulletin boards too. Many of the moms that volunteered in my classroom I still count as friends, and I've been a SAHM for 5 years.
All of the ideas below are awesome, so just jump in, and do as much as you want to do even if others aren't.