Tess's author, Thomas Hardy was a Fatalist, and Tess arguably more than any of Hardy's other novels demonstrates his literary philosophy. Most of the horrible events in Tess's life result not from her choices but rather from others' choices for her or from the environment in which she exists.
For example, while Hardy is ambiguous about what really happens between Tess and Alec, fate and Tess's parents put her in the position to meet Alec in the first place. Similarly, because Tess leaves her home village, she meets Angel, something that most likely would not have happened if not for earlier events.
The most significant argument for Tess's being controlled by fate is that no matter what decision she tries to make, her life still goes in a different (much more negative) direction. If one looks at Hardy's other characters--Eustacia in Return of the Native, the Mayor in Mayor of Casterbridge, etc.--those characters make poor and selfish choices which result in a punishment of sorts for their choices. Tess is different--she actually tries to make decent choices and tries to make the best of her continually bad circumstances, but despite all her efforts, her life still ends tragically.