Bismillahir Rahmanir Rahim.
Wa'laykum-as-Salaam wa Rahmatullahi wa Barakaatuhu.
Keeping long nails in Islam has been discouraged, and as far as the issues (masa'il) of fiqh have been concerned, there has been nothing to say that one should keep long nails.
We can see this, or we can derive meaning from the ahaadith-e-mubaarikah, which show that the Messenger of Allah (peace be upon Him) would cut His blessed fingernails and not keep them long.
Therefore, we can now ascertain that to cut the fingernails on certain days, or at certain times of the week, is a sunnah. Furthermore, that it is contravening the sunnah i.e. (khilaf-e-sunnah), to keep long nails, and to use polish on them while they are long, and to grow them in a sense where it has never been prescribed by the sunnah of the Messenger of Allah (peace be upon Him).
Let us now consider just one classical Hadith-e-Mubarikah of the Messenger of Allah (peace be upon Him):
It is narrated by Hadrat 'A'isha Siddiqah (may Allah be pleased with her), that there are ten things that constitute nature (meaning that there command was in every shar'iyyah)
1) To trim the moustache,
2) To let the beard grow,
3) To use the miswak/siwak,
4) To snuffle water into the nose,
5) To cut the nails,
6) To wash the fingertips,
7) To shave the hair under the armpits,
8) To shave all hair which is below the navel,
9) To perform 'istinja',
10) To gargle the mouth with water.
This hadith is one of the numerous ahaadith-e-Mubarikah which is mentioned in the Mishqat Sharif, that actually show that it is from nature, to do all of the above, including cutting your nails, as is specified in number five.
Because Islam is a natural religion, a religion of cleanliness, purity, and hygiene, the above mentioned things are just a part of what Islam requires, and is not the whole list.
Remember, that if Islam allowed long nails to be kept, it would have either commanded us, or the Sunnah would have specified this.
This shows that those women who keep long nails, do so that they can look after themselves the way they want and the world wants, and not in the way Islam wants.
We being Muslims must ensure that we live according to Islam, and not accord Islam to our own personal desires.
May Allah help us all to practice Islam, in the best way that we can.
Wallahu A'lamu Biththawaab.
M. Waseem Ashrafi.