My 2.25 yr. old son also wears glasses and has been wearing them for about 5 months. He too is far-sighted (6.0/6.0). From what I understand, children can "force" themselves to see even if it's difficult. Thus, she will have to re-learn to see with the glasses.
We were encouraged to keep him entertained as much as possible on the first day wearing glasses so that he didn't realize that they were on. He woke up, and we let him watch TV for the first time. He was entranced by Elmo and was able to keep them on for about 10 minutes before taking them off. Everytime he took them off, we reminded him that they would help him. Then we took him to the park, out to lunch - kept him busy for the rest of the day and he did keep them on for longer lengths (maybe 20 minutes - 30 minutes). This went on for quite a few days.
I think it took about 2 weeks for him to be completely comfortable in them. It took A LOT of activities, reminding and assuring, but he now LOVES them. We keep it by his bed and he puts them on when he wakes up, takes them off to sleep.
Give it some time and keep reminding her that she needs them. However, if she is saying that it's difficult for her to see, I wouldn't hesitate to give her a second opinion. We too were shocked at how far-sighted our son was and did get him re-evaluated to make sure.