For a start, I can recommend the following...
Any of the Bulgari Thé scents, Vert, Blanc or Rouge (if they are still being made); Bulgari Omnia Jade or Coral (my favorite is the original Omnia); my favorite Bulgari of the moment is Mon Jasmin Noir L'Eau Exquise, a soft, crisp, green fragrance, very office and all occasion appropriate. I am in love with it.
Perhaps one of the Dior Escale fragrances would work. Try Hermes' Jardin fragrances, or maybe the new floral (I forget the name). Also there is Guerlain's Aqua Allegoria Herba Fresca, Lanvin Eclat d'Arpege, L'Artisan The pour Un Ete, Chanel Cristalle Eau Verte, No.19 Poudre, No. 5 Eau Premiere.
I imagine some other people will chime in. How sweet of you to want to give your mother a new fragrance!
p.s. One I forgot that I think is very nice, and if you are in the US also very affordable: Pure White Linen Light Breeze by Estee Lauder, the pale green one. I must get a plug in for EL.
adding...I am in my 50s, so maybe near your mother's age.