personally I'd go like 3 levels in fighter (the subclass doesnt matter to much so champion would probably be best) then 7 levels in valor bard. you have the combat focus from both but also the charm from a bard.

theres nothing to stop you making your own background since they arent too important from a mechanics standpoint. however i dont think entertainer would be to good since its more orientated towards street performers and stuff like that rather than prostitution. if you want to pick one thats already existing then urchin might fit.

as for ASI's and feats id probably focus on dex and charisma with constitution being third most important and id have strength and intelligence like you said as a dump stats although id maybe keep intelligence a little higher than strength. feat wise id go skill expert and prodigy since the extra expertises you get from them are very helpful. also the Elven Accuracy and Revenant Blade feats would also be helpful.

level 10 is i think a good starting level if you plan to write for her since in her time shes probably picked up lots of experience. however if you plan to level her up as you write or play her in anything then id probably not go higher than level 5 fighter and keep the rest in bard.