I must disagree very strongly with Bonner and Rochelle. An adopted child has very different needs than a bio one, especially one that languished in an orphanage for the first months of her life! You do not want to look back on her first year at home and wish you had done it differently, wish you had spent more time and effort on attachment. You cannot get this time back and if you encounter problems in the future, you may wish you could.
At 14 months of age, there is no reason to eliminate the bottle. You should be giving it to her before sleeping - at nap and bedtime, but not letting her sleep with it. You don't want her to use the bottle to self-soothe - you want to teach her to find comfort from you. Sucking is a powerful urge and bottle-time is wonderful for bonding. She has been with you only about 1/2 her life. You need to take every opportunity you can to be her caregiver - to be the provider of nurturing and food. And the fact that she refuses milk in a cup would indicate that she wants and needs that comfort time with the bottle and you.
Both my kids, bio and adopted, were on a bottle much longer. However, I never let either of them hold the bottle or carry it. Bottle-time was only with me or daddy, before bed and usually in a rocker. Bio DD went to a sippy cup/straw cup during the day at about 11 months, but continued the night/nap bottle until she was about 2. My son, adopted from Russia at 11 months of age, was introduced to a straw cup at 12 or 13 months, but stayed on a bottle for milk at nap and bedtime. At 2.5 yrs, home over 18 months, he is still taking a bottle (in the rocker) before bed most nights. He is less interested and only wants it about 1/2 or 3/4 of the time and doesn't always finish it. I suspect he will stop completely in the next 6 months, but I will let him decide. He can have a nighttime bottle as long as he wants, but it must be in our arms - he cannot take a bottle around with him.
Whether bio or adopted, lots of kids are still using bottles or breastfeeding at 14 months. There is no reason to try to stop it, especially since she was adopted at 8.5 months and was likely neglected and without much physical comfort and cuddling during that time. And the fact that you must return to work is going to make her feel less secure - you both need that bottle time to connect and to allow her to learn that you belong to her, you are her mom, she belongs to you... especially when you will no longer be with her 24/7. Use bottle time for both of you to enjoy and relax. :) She will not go to kindergarten with a bottle!