We think our friend is lying. She said she already has a son. Does she have a mental disorder? Why is she lying?

[quietnumber944]

This is my first Q here, hope you help me.

So we think our friend is lying.
We've been friends for 3-4 years. Even tho we're friends for that long, I can't actually read what's on her mind. We're already in college, we just graduated High school a year ago and we seldom see each other.
One day, she posted something on our FB group saying that she couldn't take it anymore, that she's sick of lying to us her friends. I thought that she'd gonna confess her lies to us (like a Facebook account managed by someone who's really much like her)
After we read that post, we met to talk about her problem coz she sounded problematic. Then she told us that she's been keeping this a secret: she has a son and got pregnant during 4th yr high school. She was only 15 then.
We never noticed anything weird about her during that time so we were really shocked (and doubtful) to learn about it.
I asked a lot of questions but her answers were limited. "when did it happen?" "Where" she didn't answer.
We scheduled that we'd see her son but when the time came, we didn't see him, she said she wasn't feeling well to go to where the child was which was the "dad's" place.

I want to know, why is she telling us a lie something as big as this. I mean having a son (her parents don't know they have a "grandson") does she have a mental disorder, what is it called? Why is she lying?

Note: We love reading and writing fiction. She writes really well, and she's a very intelligent person.

[Calvin Mark]

She probably wants to brag or something. I dunno.

[Nikole]

I think maybe she feels that she isn't getting enough attention. Or just feels like you guys are getting bored of her.