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.
A woman is considered Mahram (permanently unmarriageable) to a man for one of three reasons:
The Kuwaiti Fiqh Encyclopedia reads, “The reason for being a Mahram is due either to blood relation, or breastfeeding, or relationship by marriage.”
Therefore, the woman who raised your wife is not considered a Mahram to you.
For more benefit about the women who are Mahram to a man, please refer to fatwa 85868.
Allah knows best.