From what we've seen until now, a lot of the situation stems from a communication problem on Seniannas side. The situation DID get better when she started to at least partially communicate her troubles and not keep it to herself.
First of all, I hate suiciders. In my eyes they're the biggest cowards, taking the egotistical, easy way out of their problems.
That said, she attempted it multiple times and nobody really cared, of course she'd think nobody actually cares about her.
But as much as you can call them terrible, you have to realize that mental problems are hard to detect. The way she acted before the reincarnation could very well have been mistaken for a bad personality, the suicide attempts for attention seeking. Them not taking it seriously is a valid criticism, but if the other person doesn't tell them shit, how could they ever understand the meaning behind these actions? Nowadays, with all the knowledge and awareness we have it's much easier to discern, but you also have to keep in mind that Psychology is still in it's infancy in our real world, can't expect much from a rather medieval setting then.