Whitney wasn't a secret lesbian
I think the only reason Cissy disliked Robin is because she didn't know if it was a friendship or something more, and that probably scared her.
There's nothing wrong with what she answered Oprah's question "If Whitney was gay would you have liked it." She's an old school church woman and they are STERN in their old school beliefs

I don't think it makes her a homophobe though.
Whitney stopped her friendship with Robin once she married Bobby. She chose her marriage over her friendship and that is why they became distant friends overtime.