Ideally, she should have stopped him before he left Randhawa house. She overheard his conversation with Bua, she knew he was up to something and it wouldn't be good for Zaveris. If she wanted to make him do the right thing then too it would be better to discuss things at their house instead of running off to Zaveri house simply because Sneha asked for her help.
I don't care if Prarthana wants to walk out of this marriage or if she wants to ignore Shivansh, that's her right. But she must learn to prioritize herself and not send mixed signals. She should not run off to protect the Zaveris from Shivansh's wrath, that's not her concern. If she cares about Shivansh's feelings, his moral rights and wrongs, she should remember both his reasoning behind this revenge and their (PraShiv's) present situation ( + Pranak's past). There is no reason for her to be loyal to the Zaveris, that's not her family. She answered Sneha's call for help, but her need to save them came across as her care for them and not Shivansh's heart / relationship.
And if she cares about her feelings, then she should pick a side (even if it is her side, with both Raunak and Shivansh out of her life) and stick to it instead of trying to balance her past and present duties with respect to the Zaveris and Randhawas.
The other day, with Raunak, she did not say that it was her decision to stay of leave or do whatever and until she says so, he can't barge into her bedroom and demand she leave Shivansh. She doesn't need his rescuing. Raunak might be obsessive and he's definitely stupid but he has good reasons to be worried for her, he doesn't know that Shivansh is good or that he cares, nor does he know about the kidnapping.
Prarthana, on the other hand, knows that she is willing to give their marriage a try, provided that Shivansh is also interested (we know, Prarthana knows, Bua knows, even Shivansh knows, although he won't admit, that he's giving it a fair chance unless something happens). She should say that to everyone involved. And she should focus on her life because right now it looks like she's trying to fix two families ― Shivansh's because he is her husband, and Smita's / Raunak's (depending on who you ask) because she is loyal to and cares about the Zaveris.
I don't mind ITV's fix-it-all FLs when they are trying to do it for their family, but....yeah, I didn't like her trying to stop him from throwing out the Zaveris and doing it in front of them.
564