As of the above conversation regarding my marriage with a girl whose mother has an extra maritial affair.

I wish to know more about it.

I have heard in qutba and majlis by our scholars (maulanas) that even islamically the child inherits all the good and bad qualities of the mother. Which is why Imam Ali a.s. was looking for a brave family to gett married after Bibi Fatemah Zehra a.s

In this case, where the mother is on deen, believes in Quran and the Prophet, but still have some major bad qualities which would be bad for our future if her daughter (my to be wife) inherits those qualities

Is it still okay to go about with this marriage.

The girl is of good aqhlaq and has assured me about her doings and deen.

Please Suggest.

Yes child will inherits good and bad qualities. But in some cases some child’s learn good things from the society.
If you are in doubt then don’t marry with her. discus the issue with family
Try the find momina girl she will be better option for you, your family and generation.