" Does it mean Raelina is a combination the real Beatrice and Eunha? "
Not a combination: Our current Raeliana (Eunha) is the real Beatrice
I think it was mentioned in the previous chapters (comment section) : iirc that if OG Rae didnt screw up the novel - Eunha should be transported to Beatrice body but OG Rae had to deal with the witch (responsible for the body swapping) thus OG Rae transported to Beatrice, while OG Bea(Eunha) transported to Rae's 
but if you're asking for the OG Bea(before either OG Rae or Eunha) - that's we don't know - might be a empty vessel. Technically the novel "starts" when Raeliana dies in the novel so Beatrice "appears" is the novel