I think improving by 300-400 points in that time is unrealistic, but she can improve. My DS20 found the Khan Academy practice to be super helpful, and he was able to improve his score by 100 pts in about 6 weeks.
If your daughter took the PSAT and has a college board account, she will be able to link her college board and khan academy accounts so that the practice she does is tailored to the areas she had a harder time with. You can choose how many days per week and for how much time per day you want to practice, and it sets the whole schedule up for you.
Also, it’s not unusual for kids to take these tests more than once, so if she’s not happy with her score in March, she can take it again. My son took it at school last March for the first time, spent some time practicing, then took it again in June for the last time.