All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
It is not permissible for this woman to marry herself off without the permission of her guardian; neither is it permissible for anyone to marry her off or marry with her without the consent of her guardian. ‘Aa’ishah narrated that the Prophet said: “A woman who marries herself off without her guardian's permission, her marriage is null and void, her marriage is null and void, her marriage is null and void.” [Ahmad and Abu Daawood]
If a woman does not have a guardian or his authorized deputy, then a judge of an Islamic court can marry her off. The Prophet said: “The ruler is the guardian of every woman who does not have a guardian.” [Ahmad and Abu Daawood]
For more benefit in this regard, please refer to Fatwa 83338.
Know that it is the bridegroom who has to pay the Mahr (bridal money) not the bride. However, being easy in the matter of Mahr is better.
If she does not find a religious, suitable husband, then she has to be patient and ask Allah to help her and grant her a good husband. You are not responsible to marry her off or even to bear the expenses of her marriage. However, it is desirable to help her to get married and Allah will never spoil the deeds of good doers.
Allah knows best.