Looking back in the archive files, I think there could be more to Melissa than it meets the eye.
Melissa's letter towards Bella in Archive 13 implied that Melissa and Sam's mother doesn't get along.
"It's Mommy. I'm not sure if Grandma will want you to read this letter or not, but I'm writing because I miss you so much."
They either had a huge falling out with Sam's mother having the idea that Melissa was abandoing her daughter for the sake of her career, or perhaps Melissa lost her temper towards Bella and Sam's mother just happened to be a witness.
Melissa's temper is obvious in the story, but she doesn't seem to be the kind to get angry towards Bella in the same way she does towards Sam. In the video footage from Archive 2 when she scolds Bella for chewing her nails, she doesn't sound as angry as she was towards Sam, but that's just me.
Reading the last section of Archive 13 gives the implication that Melissa cannot be with her daughter unless she changes her ways first:
"I'm so sorry we can't be together. I've missed so much time with you, and there's no way I will ever be able to make that up, but just always remember that Mommy loves you more than anything in this whole world."
But then again, maybe I'm just looking too deep in all this. Who knows?