First please try to ascertain discreetly how the classmates of your child feel about the school work,study, home assignments etc. Just get an idea how they manage or cope up with the pressure. You can have discreet and diplomatic interaction with the children and direct discussion with the parents. If all of them are under such pressure, then take up the matter with the school teachers and principal and try find a generally acceptable solution.
However, if you infer that it is a particular issue only with your child, then you have to take personal efforts to understand the root cause and find a practical solution.
As soon as the child comes from school, give her the needed food and drink and engage her in conversation about matter which may bring down her pressure. Like how the household pets(if any) acted in her absence, who all visited you,who all telephoned you etc. Then you may slowly ask how was her day, whose birthday was on that day, how they did, you may ask how the food (if any) she had taken from home tasted,what improvements or variety she wants etc.
Then sit down with her and help her to finish at least a part of the home assignments given. Take up those which she is more comfortable and can finish soon.
Then allow her to engage in her interesting play or game activities, or watching TV or talking to her classmates and friends. Call her back after a reasonable time. Let her get refreshed by a bath with warm water and make her finish her assignments before the next time food. If there is sufficient time ask her and help her to study what was taught that day. Then again have some family conversation at the dining place. Do not take up anything related to study then. After food allow her to study and go with her and help her if she needs. Let her arrange the books exceeded for next day. If some time is available let her glance on the topics that may be taken at the class next day.
Use holidays to spend more time for review and repeat study. Once in a while allow one of her friends(preferably one having better grades) to be with her on a holiday study and to help her. Let them also play together for sometime too.
Please be flexible and understanding for the initial couple of weeks till she gets used to the routine. Monitor how she feels . If improvement is there stick to the same regimen. If not, make some amendments asking her feedback and suggestion also. Make her feel that study also is pleasure giving and essential.
Interact with her teachers to know how she fares and what improvement has come and what is needed.
These will make positive results.