Praise be to Allah.
So long as your sister repented to Allaah for what she did of trying to commit suicide, there is the hope that she may be forgiven. Repentance wipes out what came before it, and the one who repents from sin is like one who did not sin at all, as was narrated in saheeh ahaadeeth from the Prophet (peace and blessings of Allaah be upon him). If you give in charity on her behalf or pray for forgiveness for her or make du’aa’ for her, that is good; it will benefit her and you will be rewarded for it. You have to fulfil the vows you made to do those acts of worship, because Allaah has praised those who fulfil their vows in the verse in which He praises the righteous:
“They (are those who) fulfil (their) vows, and they fear a Day whose evil will be wide-spreading”
[al-Insaan 76:7 – interpretation of the meaning]
And the Prophet (peace and blessings of Allaah be upon him) said: “Whoever vows to obey Allaah, let him obey Him, and whoever vows to disobey Allaah, then he should not disobey Him.” (Narrated by Imam al-Bukhaari in his Saheeh)