For women, it is trendy to keep their fingernails long and in nice shape.
Many women find that nailpolish looks better with long fingernails, which makes them grow their nails.
Many women, and people in general, grow their fingernails after stopping the bad habit of biting them. See Why some people bite their nails
Having long nails for women is sometimes useful in opening things. See Why do guys grow their pinky nail long
Some women find that growing their nails is easier than having to trim them every couple of days.
Some women like to grow their fingernails because it makes the fingers themselves look longer.
Many women believe that growing their fingernails is a feminine thing to do, unlike keeping them short which is commonly associated with men.
Long fingernails are easier to clean and to be kept dirt-free than short nails.
Some people find long fingernails more attractive and sexier than short ones, which can motivate some women to keep their fingernails long.
It is trendy and fashionable nowadays to do nail art, which usually requires long fingernails.
Some women prefer to keep their fingernails so they can comfortably scratch parts of their body.
In some cultures, especially in the past, having long fingernails meant the woman was from a high social status.