Lowkey, I don't see her as very very protective, but like just trying to warn her younger brother. I could understand that she may be a little overprotective but I don't think it's that much? I'm an older sibling to two younger brothers so I can see her reasoning for some of her protective behaviors. I do find that she's trying to stop her brother from kissing his bf a little bit weird because she also has bf, but other behaviors such as making sure he doesn't go out without telling her and where he goes is pretty normal, no? I mean even the kissing bit, you wouldn't wanna see your sibling kiss their partner, and I'm assuming that Rak hasn't seen Babe kiss Dom much because before the fifth episode he hasn't even thought of kissing Fah. Also, Rak is very naive and pretty unaware and I'm sure that she just doesn't want her younger brother to get hurt from a broken heart. But then again I feel like she should just support him through his relationship rather than shield him from it, like what she's doing. Other than the relationship overprotectiveness, I think other factors are very normal for an older and younger sibling dynamic.
Overall, I find that Babe is not that overprotective but instead just worried for her only sweet younger brother, though I do find her not allowing to be intimate with his bf a little weird when she also has a bf.