Jessica,
Being treasurer is a thankless job. I always felt terrible for our treasurer when I served on executive board. She was constantly trying to smooth over hurt feelings with sisters who had a problem with a fine or other financial issue.
My best advice is to remind the girls upfront that you personally are not responsible for their fines. THEY are! Let them know that you intend to do your job accurately, and that you will not play favorites. Remind them that they made a financial commitment to Delta Zeta when they first pledged and that it is one of 3 major obligations that they agreed to uphold in order to be a sister in good standing.
Lean on your exec members for support if necessary, and vent to them when you have to. That's what they are there for!
Good luck, sweetie!
DZ Love,
Carrie