They want her to retake the GMAT?

[clashingtime]

So, my friend took the GMAT about a month ago- but she was having an awful day and it ended up going really badly, so she got just below a 500 on it. She went ahead and applied to a few MBA programs, and the admission committee emailed her from one school offering her to retake the GMAT to make her application a little stronger. They told her she still has until early May to retake it, so there's plenty of time for her to study and work towards a better score.

She just wanted to ask if this was normal, and how much it would really improve her chances if she retook it. Thanks!