At 4 years old the child is still gaining control of her fine motor skills in her hands. Most 3 year olds are still using motions that come from their shoulders and elbow areas, with pencils, crayons and markers being held with the whole hand. At 4 she should be able to gain this skill and by the time she starts Kindergarten she should have it Mastered. Just keep helping her, she is NOT supposed to be able to make perfect letters ant this age, she will learn that as she gets older.
My four year old child care class did a lot of tracing things, in sand, in pudding on finger paint paper, in other mediums, so they would feel successful and not frustrated so much. We had foam letters that the alphabet were cut out of and they were rather big,maybe 5"X7", or a little bigger. We also had shapes and things, like a car or house.
This way they could trace around the edges and see what they had done and it usually looked just like the letter or shape they were trying to make.