Bism Illah wa assalaamu alaykum wa Rahmatullahi wa Barakatuh.
Consider this scenario. You know of a sister who has not been praying or wearing any form of hijab. She asks for some Islamic clothing and hijab. You know that she has not worn any hijab consistently for years and shaytaan whispers to you that she is probably asking you so that you will have a better opinion of her or think she really is trying to improve but prevented by a lack of suitable clothing. shaytaan whispers that she will probably not wear what you give her much, or for long, and it will probably end up dusty in the closet or thrown away.
Audhu b'Illahi min as-shaytaan ir-rajeem!
Give her good hijab. Give her things from your collection that you particularly think she will like, or will suit her. This will encourage her towards modest dress. Give her a nice quality aba'a (abaya), a good khimar - things you would wear yourself to Jumu'ah or Eid.
Give your best, Allah will do the rest.
The sister will feel that you have honored her by giving her nice things. It will open her heart to you and give your da'wah a smoother reception bi idhn Illah ta'ala. She will taste the beauty of Islam, the practice of loving for others what one loves for oneself. And for you, you will have lived the beauty of Islam. You will have lived loving for another what you love for yourself. You will have lived Ihsaan, giving your best knowing that Allah is watching you. You will have lived giving the sister her rights of husn-u-thann, having the best suspicions about her. She may well live up to those expectations, inshaa Allah. You will have triumphed over shaytaan and his evil whispers.
Regardless of what happens to those donated clothes, giving your best elicits the best from yourself and from Allah, subhaana wa ta'ala.
So give your best, Allah will do the rest.
Subhaanak Allahumma wa bihamdik, laa ilaaha illa ant, astaghfiruka wa atoobu ilayk.