I’d say, yes, she’s probably on Facebook to feel less alone in the world.
There’s this thing called the hierarchy of needs. This is what it looks like:
So, you’re mixing up what she needs with what you need. Most people we encounter have our physiological needs met, i.e. roof over our heads and not currently hungry. We’re also relatively safe, some more than others, of course. Meaning most people are looking for love / belonging.
You’re talking to her as if she wants what you want, esteem. Because the advice you are giving her is typically what you’d do to earn people’s esteem.
She’s not taking your advice because she wants to feel loved, she doesn’t have the head space to chase esteem. You just talking to her helps alleviate her loneliness.
The sad thing about our society is that we withhold love from people until they have earned our esteem. This is ultimately why we fat-shame and say people are just looking for attention.
What your friend needs is a support group. If you really want to help her, find one and have them reach out to her.