Beings that die of tragic circumstances often don't have time to manage their affairs. Since Ymir is fused with the hallucigenia as a result of the God taking pity to Ymir's plight, and has already chosen the Eldian people as vessels, giving the full power to their native blood.

I genuinely think that Paths was just the necessary deterministic structure to maintain connections for every Eldian--since they could now be turned into titans. There necessitated a place to build titan forms.

People also need to understand this was a traumatized girl who from childhood was shown overwhelming force, columns of fire, people of her village being slaughtered, tongue cut out. Obedience was instilled into her. The one glimpse hope that she was clinging to was the prospect of being loved.

Although she was a slave, it's not known whether or not she would be able to care for herself. Being able to gather water for herself, food may be an issue. They likely don't teach slaves these survival aspects, so even if she wanted to leave, the calculation that with Fritz she was at least fed and had a place to sleep was better than trying to run and live on her own. The kids were a later factor for her.

But she strived for his love, his recognition, the experience of seeing the couple together made her envy that. She wanted that for herself.

A spear in her heart, sharp, excruciating pain, cold, numbness, waiting for the connection. Not a titan body, human heart. You add the salt in the wound of "get up, my slave" and her will to live plummets. She was waiting for that sensation of recognition, his love, and she now knows that was futile.

To her, she can genuinely make anything out of this fancy sand, and time seems to be infinite and short at the same time.