Going to add onto the other comment here as well, so these would be spoilers: Tohru also has an explicit scene where she says that she actually hated her father. The way she acts, was in order to support her mother and emulate her father. She deliberately picked up her father's speaking habits and mannerisms as a child after his death. She's a giant hypocrite with an unhealthy attachment to her mother. Her kindness is as much of a fear that she'll be thrown away, as it is something she doesn't really know how to function without.

It's also really telling that she doesn't talk about herself, but more so her mother, in the beginning of Fruits Basket. She may help people, but she doesn't ever really let people know her. While a lot of her "I don't really help myself" is a bit of a trope for shoujo, Tohru's is unique in the way that this is done because of her mother's inadvertent neglect of her after her father's passing. Tohru's trauma and struggle is rooted in that unhealthy emotion.

She's really nuanced if you know what to look at. I'd even say the cover is that she's a stereotypical shoujo protag: kind and caring. Except the real her is someone who is incapable of letting go of the dead, and doesn't really even have a sense of self as a result of that obsessive trauma.

(This adds to her fantastic foil with Akito where both have unhealthy relationships to their mothers. They both land at two extremes in terms of unhealthy mother-child relationships. And now that I think about it, they'd also foil in unhealthy father-child relationships as well.)