"Al-Wala' is to the one who did the favor (of setting the slave free)." The Messenger of Allah gave her the choice, as her husband was a slave. And she gave some meat to 'Aishah as a gift, and the Messenger of Allah said: "Why don't you give me some of this meat?" 'Aishah said: "It was given in charity to Barirah." He said: "It is a charity for her, and a gift for us." (Using translation from Nasāʾī 3453)
أَنَّهَا اشْتَرَتْ بَرِيرَةَ مِنْ نَاسٍ مِنَ الْأَنْصَارِ فَاشْتَرَطُوا الْوَلَاءَ فَقَالَ رَسُولُ اللهِ ﷺ الْوَلَاءُ لِمَنْ وَلِي النِّعْمَةَ قَالَ وَخَيَّرَهَا رَسُولُ اللهِ ﷺ وَكَانَ زَوْجُهَا عَبْدًا فَأَهْدَتْ إِلَى عَائِشَةَ لَحْمًا فَقَالَ رَسُولُ اللهِ ﷺ لَوْ صَنَعْتُمْ لَنَا مِنْ هَذَا اللَّحْمِ؟ فَقَالَتْ عَائِشَةُ تُصُدِّقَ بِهِ عَلَى بَرِيرَةَ فَقَالَ هُوَ عَلَيْهَا صَدَقَةٌ وَهُوَ لَنَا هَدِيَّةٌ