You don't have to wean her just because you're going back to work, or because she's turning one. They continue to get benefit from breast milk, getting sick MUCH less, and many of the benefits they receive are a 'dose response' which means the longer they are breastfed, the greater the benefit (higher IQ is a dose response)
You can still nurse her in the mornings, when you come home from work, and before bed. She still may need it emotionally, since right now it meets both nutritional and emotional needs.
If you do wean, do it slowly, replacing one feeding at a time for a period of time, and usually leaving morning and night feedings until last.
Try different sippy cups, try them often. Let her experiment and play. Let her get wet. She will catch on.
Also, some children at this age will only eat solids during the day and wait for mom to get home to nurse a bunch. This is fine, and nutritionally sound. She may feed again before bed and in the morning. She can get breastmilk smoothies at her daycare provider (scrape frozen breasmilk much like an italian icee) so it can be spoonfed.
It doesn't have to be all or nothing. She can still continue to benefit from your milk. Your milk continues to be an excellent source of nutrition for years, it doesn't magically change at 12 months (other than the typical changing to meet your baby's needs).
Take your time with weaning. Contact your local La Leche League. They likely have books you can borrow from them that are all about the weaning process. www.llli.org
Good luck!