She is nearing 30, but she need to be home before midnight. There's 2 issues here. The first is that, if she goes home late, she'll be reprimanded by her parents. This is because her mum will wait for her till she come home. So the later that she come home, the less that her mum sleep. In addition to that, her mum is worried about her. She says that parents will always view their child as children no matter what the age. They'll always be worried about them. So she tried as much as possible to be a good girl and go home early. She cannot stay, out before seeking her parents permission, which is always accompanied by a solid reason.
While her filial piety is admirable, I think she's doing it the wrong way. I feel should make her parents realize that she's no longer a small kid and that she's capable of looking after herself. Her parents have to stop waiting for her at night and not control the time that she should come home. If she wants to stay out, for whatever reason, they should trust her to not get into trouble. Even if she did, they should accept that she's her own girl now. Respect her decision on how she wants to run her life. She has to make her parents realize that.
Of course, I don't mean for her to be out late every night. It's her freedom that is the issue here. And also, it's not good for her parents to wait for her. They should be sleeping when it's time to sleep. By being a good girl now, she is actually depriving her mum of a good night's sleep. I am all for yelling at her mum for now if it makes her get the idea. It may be rude, but it's for her mum good. so it's justified.
The second is that her mum cooks her dinner everyday. And she has to finish them. Or else it's a waste of money and effort. So when she are with friends for dinner, she won't eat. She'll wait till she's home and then eat the food that her mum prepared for her. If she went home at 1am, she have her dinner at 1am. There is 2 problems here. Having a heavy meal before bed time is not a healthy thing. This may cause as to gain weight and more importantly, it makes our body work to digest our food when it should be resting during sleep. And when she have her dinner at such a weird time, it makes her body confused about her eating habits. Another bad thing. It's good to be appreciative of your parents. But doing it at the expense of your own body is simply wrong. I am sure the parents don't want that, though they may not understand the concept of it's bad having dinner at 1 am.
I feel she should just have her dinner as usual when she's out. And not take the food that her mum prepared for her. It's a waste, no doubt. But after a few times, she probably won't cook for her when she say she's out. This is the right way to prevent her mother's efforts from going ot waste. That is to make her make unnecessary efforts.