My guess is, she has just started living alone. Away from
her parents for the first time, she has to shop and cook for
herself - which she probably did not do very often when she was
living with her parents. She has therefore a lot to learn from
daily life, and she realized that education can happen outside
of school too.
The most exciting thing for her was not school but her single
life. "The price of vegetables" is nothing but a symbol
of a single life, here. Her father was expecting some different
answer like the joy of studying at university, and couldn't understand
what his daughter was saying.
To begin with, he thinks, just like other people of his generation,
that education happens only at school; "school equals scholarship
equals education." And, this is the way to move up in Japanese
society. To be highly educated is a good strategy, and so he
invested in his daughter (university education is not free).
Naturally, he expected his daughter to study something scholarly.
But her answer was not about scholarship. Now, if his daughter
doesn't study, his investment becomes meaningless - that's why
I also think that he is like most men of his generation. He
didn't do any housekeeping! When he was young, his mother cooked
for him, and did everything else. And, after he got married,
it was his wife. So he is not aware that housework demands some
intelligence. Naturally, he can't understand why his daughter
is so excited about shopping for vegetables.
His daughter, who understands well her father's way of thinking,
answered, "the price of vegetables." It doesn't mean
she didn't study; she just didn't want to give him the answer
he was expecting.