Radhika was going to act like that as it is consistent with her character. The problem is how they showed her today and Dev too for that matter. So if somebody has watched her from the beginning and understood her character, they would understand her motivation. Radhika has always let her excessive emotions for Dev cloud her judgment. Her judgment was clouded when she came as a fake wife, then again when Rohan blackmailed her and she didn't tell Dev and instead went to Rohan's room during the SR and now again where she has let RP brainwash her to the extent that she is thinking that she is going to jeopardize Dev's bright future.
Yes Chalhov and here she is wrong...I mean not considering the depth of his emotions and his feelings but Dev also did the same thing to her in the past...Dev was letting his obligation clouding his judgment when Radhika went pleading to him and here Radhika is letting her fear clouding her judgement.