Sure its normal, actually very common. Not saying its really healthy for her long term, being essentially a lazy sponge but it is normal. I suggest, however, you stop subsidizing her and this lazy lifestyle. If they insist that you pay every time you go out with them then stop going out with them, eat in, save your money and go get a place to rent when you are able - you should probably (you don't mention your age, just guessing here) be moving out anyhow.
She is making lame excuses because she likes sitting around being lazy and if your father is willing to earn enough money to support her that's fine, and not your problem but you shouldn't have to support her - you need to be looking towards your future.