Yes, there is a danger of spoilers, however, I think I will try to explain this without running ahead of things here...

JA makes this deliberate use of the word "Heroine" somewhat sarcastically, meaning that our Catherine is different from heroines of novels in circulation at the time, "Cecilia, Camilla, Evelina, and others. She makes this difference abundently clear whenever possible, which the following passage from chapter 1 indicates.

She had a thin awkward figure, a sallow skin without colour, dark
lank hair, and strong features--so much for her person; and not
less unpropitious for heroism seemed her mind. She was fond of
all boy's plays, and greatly preferred cricket not merely to dolls,
but to the more heroic enjoyments of infancy, nursing a dormouse,
feeding a canary-bird, or watering a rose-bush. Indeed she had no
taste for a garden; and if she gathered flowers at all, it was chiefly
for the pleasure of mischief--at least so it was conjectured from
her always preferring those which she was forbidden to take..."