So... the point of Rae as a character is that, since she's a succubus, she would like everybody? If, instead of MC, she would be at the house with any other people in the earth, she would like him/she just the same because she's a succubus? And the same with the other girls, because there is a succubus around? I don't think that would be a good trait for any character, at all. In that case, it doesn´t matter the choices of MC or the kind of person he is, he will get all the girls eventually anyway...
About Rae being a warrior, she's the smallest person of the house. It´s just absurd, she doesn't have the physical strength. And yes, since she's an imaginary character, the dev can give her any trait he wants. She could fly and have lasers in the eyes, for example. But there are rules and conventions even with imaginary characters. A vampire sucks blood, sleeps during daylight and hates crucifixes. A werewolf transforms in full moon nights and becomes an irrational beast that could kill anybody. Other than that is corrupting the archetype of the character. That's why a lot of people hates "Twilight", for example. And a succubus uses her charm and sex appeal to get her way, no physical strength.
The dev wants to make her a 4.7 feet tall, 90 lbs. Bruce Lee? Well, he can, but it's absurd and it doesn't add to the character. She's even more interesting if she's weak, but she trust in her intelligence and appeal to succeed in all kinds of dangerous situations, as an infernal Mata Hari. If it's important for the plot that MC trains as a fighter (although, so far, it isn't), he could train at the house with the 6.5 feet tall 200 lbs. pirate butch, for example. It would make way more sense.