no, her daughter staying in the phils will make no difference to your g/f's visa app, your sponsoring just your g/fs visa app not her daughters, many on here have left thier kids in the phils and successfully applied for a settlement visa at a later date for them, i've done it myself with my stepson.
i wouldn't bother mentioning the father, like i said your not applying for a visa for her daughter (yet). thou i would mention, your g/f's parents will be looking after the child, as she has little or no contct with her father and your g/f will be financially supporting her daughter as well as making many of the decisions which effect her.
no, you will only need to worry about supporting your g/f, as at this moment in time, your only sponsoring her visa app. you will only need to worry about her daughter, if and when you apply for a settlement visa for her, and by that time you both would be settled and be married, and possibly your wife could be working by then.
what you've said should be fine, but i would mention that she has little or no contact with the father, and her parents will be taking care of her, but your g/f will still be supporting her financially and emtionally ???? does your g/f thou ??
being vague might be good, becuase i wouldn't want your g/f to lie about her plans for her daughter, but unless shes 100% sure she will not want her to live with you, i dont think you have much choice but try to keep your options open. becuase if you put on the visa app that her parents will be looking after her for good, and then she changings her mind, the embassy could look at her orginal visa app.
so keep a copy of the visa app, even better scan it in, and if you do apply for a visa for her daughter, you can send a copy of the visa app of your g/fs stating you may want her daughter to settle in the uk.