One thing for me that really sticks out is how much she immediately clings to the MC whether you go for a friendship or romance route.

She latches onto any immediate similarities you have.

You're both ten

You're both new

Maybe you both wear scarves

Maybe you both really like being outdoors

She immediately declares any color(s) you like are also her favorites before you even tell her what your favorite color is

If you tell Mrs. Murray you want a window seat, Tamarack also wants a window seat so you can be the same. Once she's told she can't both sit with you and have the window seat, she says "But I want to be by them..." (crushes)/"How are we supposed to talk!?" (friends)

She immediately tells her grandmother you're her best friend or her favorite person. She tells you resolutely your second day of knowing each other, that you're going to be her best friend forever. That she wants you to be in her life forever.

And it's like, once you finally start learning more about Tamarack ー her parents leaving her with her grandparents, her parents and grandparents constantly fighting, she was homeschooled until she moved to Golden Grove, she isn't good at making friends with other kids, most of the kids in your class are put off by how loud and intense she is (Renee included, even though in Step 1, Tamarack being a girl already puts her off on the bad foot with Ren to begin with) ー it makes perfect sense why she clings your character.

It becomes painfully obvious with every piece of information you learn about Tamarack Baumann, that you're the closest thing to stable she feels she has. So of course she clings to you, she wants to do things together, she wants to latch onto your similarities. In her Step 1 eyes, these are things she feels will keep you in her life.

So it feels like, the more mutually enthusiastic your MC is about her, the more it adds to the sense of stability your character provides.

For all we know in Step 2, this could be even more the truth. Of course, she's lost a lot more of her high energy tendencies, she's a lot more shy and insecure, but should you decide to remain friends/crushes with her going into Step 2, the MC probably provides so much comfort and stability for her.

You're still her best friend, you're still her person.

You promised your second day of knowing each other that you would be best friends forever and you kept that promise, contrast to her parents who can never seem to decisively choose when to come get her. She loves her grandparents, but despite knowing her grandparents love and adore her she probably feels that it's ultimately familial obligation that they have her with them.

Family isn't something you get to pick but you chose her; you've constantly chosen her and she chooses you back full-heartedly.

Should you be friends/best friends/crushes with Tamarack, you probably mean more to Tamarack than she can properly express at the time.