Make sure your daughter is getting enough sleep. She should have a definite routine--go to bed the same time every night, get up in the morning at the same time every day. Lack of enough sleep is something that can really affect concentration in school.
Make sure she has a place to do her school homework which is free from distractions and noise. Check her homework to see if she finishes her assignments and if she works in an organized manner. Encourage her to recheck her homework for errors. Ask her questions about her homework assignments to help stimulate her interest in the subject matter. Talk to her about school every day. What did she enjoy most that day? What interested her, what bored her? Encourage her to take notes about what the teacher says--taking notes encourages more active listening and concentration. Ask her to set some goals for herself in school and write them down. Help her develop a plan to reach those goals. After she has done this, promise her some reward for each goal she is able to achieve. It doesn't have to be a big reward, but it does have to be something she likes, or wants, or enjoys. It is very important to reward progress, and you want to encourage her motivation to try to do better in school. Ask her teacher for more specific suggestions for what you might do to help your daughter with her schoolwork. Really pin the teacher down on what needs to be improved and what you can do to help. Is the problem only concentration, or is it also motivation?
No matter where you are with your daughter, even a simple shopping trip, talk to her and encourage her to notice things around her. Point interesting things out to her. Encourage her to point things out to you. You want her to pay attention to things all the time, not just in school. If you watch a movie or a TV show together, talk about it and ask her questions about it, and share your ideas and thoughts with her. Help her to become an active listener who thinks about what is being said and develops curiosity and asks questions. This will help her in the classroom where she has to pay attention to what is being said.
Help your daughter to develop some hobbies that require concentration and practice skills. Making something, like simple jewelry or working on a crafts project, or learning a sport, or playing a musical instrument, or even playing games that enhance concentration. Let her improve her concentration skills by working on something she enjoys, and something which will allow her to see progress. Encourage her to read books she enjoys in her free time, and make regular trips to the library with her. Reading depends on concentration, but can also help to improve it. Get her some puzzle books or age-appropriate crossword or word puzzle books. Those also help concentration skills. Limit TV viewing so she can get involved in things which require more active concentration and effort. Encourage her to write stories, or poems, or draw pictures, and get her a special scrapbook or binder to save her work.
As long as your daughter is "healthy, smart, funny, normal and sweet", I don't think you have a lot to worry about. But you do want her to do well in school, as well as she can, and you want her to develop the skills that will help her. Concentration, motivation, good study habits, are all things that can be learned or improved. Anything you can do to help your daughter with these things will help her at school.