I think Suhana and Golu locking Ayush in a room has been set up to incite Ishwari to spew venom at Suhana. Till now, we've seen her 'soft' favouritism towards Ayush. She has been showering him with attention but was maintaining a civil yet detached facade for Suhana. However, this incident will probably bring out her claws and she will end up saying very hurtful things to Suhana, perhaps even bringing up her not being 'apna khoon'.
We saw a glimpse of this when she told Sonakshi after the mug kaand that she is an unlucky mother because her first born turned out to not be hers. Even if things don't go that far, I am sure Ishwari will definitely end up amplifying Suhana's insecurities. Will be interesting to see how Dev reacts to it.