Yeah, that actress has NO boobs. It's a very common flaw in cosplay, IMO, to build an outfit exactly like it is on a drawn, mis-proportioned, unreal character. It can take away from the overall look and feel of a character when real hips, boobs or waistline interfere in such a way as to make an ordinary girl look chunky, or too short, or too tall or whatever. It becomes "OMG why is she trying to play X?" instead of conveying "hey look! Soandso!". Fitting a costume to your body is always a good choice.
You want to convey the character, not have people say "OMG boobies!", a literal translation (having the neckline plunge to the same place on you that it does on her) is likely not the best option here. Sure, it needs a deep V, but it will read the same way while still allowing you the support you need if it doesn't go down as far. it will also defer unwanted attention.
Wear a bra, don't have the neckline plunge that deep.