Nicole is clearly creating distance with Ngozi out of fear of being abandoned or hurt again. This could just be down to Rosie straight up leaving after finding out the Down Syndrome diagnosis, but it’s been hinted at she has some deeper history with Rosie.
Rosie blamed her for whatever happened that made her end up in a wheelchair, and Nicole only takes on the surrogacy out of guilt.
Perhaps Nicole feels unworthy of such love from Ngozi because she feels like such a horrible person for whatever happened in the past. Maybe she is also afraid of getting too close to Ngozi in case she ends up getting hurt too, just like she hurt Rosie.