We learn about Mattie's feelings directly and indirectly. In chapter 1, Mattie arrives for the first time in Starkfield to take care of her far cousin who is Ethan Frome's sickly wife, Zeena.
Mattie is a young, pretty and impressionable girl whose warm personality and bubbly excitability contrast tremendously with the cold, isolated and barren Starkfield.
Yet, Mattie's life is a bit deeper than what meets the eye. From what we learn, her father was once a wealthy man, so Mattie did live a life of luxury. Yet, after her father and mother died, leaving her a mere 50 dollars, it is assumed that they squandered all their money and even stole from Mattie's poorer, current caretakers. She was kind of like a problem to them, which is why they gladly accepted Zeena's proposition of taking her as an unpaid help.
Keep in mind that, all this being said, Mattie is in a sad situation: her joie de vivre, her hunger for life, and her youth has already met with disdainful and sad moments. Her nearby town of Stamford is perhaps just as isolated as Starkfield considering that the latter is a truly isolated place, and Stamford is the relatively closest one.
Mattie does not explain directly what her views are on Starkfield, but she does speak about her nights when she can go out, and of her feelings for Ethan; this is, of course before their fatal accident. We really do not know what happens afterward as far as emotions go.
Regardless, we are not aware about Mattie's suicide plans until she actually talks about it, unbeknownst to the reader whether she had planned it ahead, or on the spot. Knowing that she literally has nowhere to go, and no marriageable prospects to feel comfortable with, her only way out is through death. In chapter 9, the conversation about death comes out in the open.
“I don't know how it is you make me feel, Matt. I'd a'most rather have you dead than that!”
“Oh, I wish I was, I wish I was!” she sobbed...
“Don't let's talk that way,” he whispered.
“Why shouldn't we, when it's true? I've been wishing it every minute of the day.”
Therefore, from her behavior in the house, to the enjoyment of her minor entertainments, we could argue that Mattie just went through life as best as she could, knowing well that the present time is all that she had. When she sees that even that has been taken away, she claims that she has planned to be dead all day long. We can deduct that Mattie has covered a life of disillusion and unhappiness by attaching herself with the few gifts that youth still can offer: hope, fascination with new things, and the joy of a potential first love.