Is it normal i feel she was just filling in her time?

Quite confused and hurt despite this being "no big deal" to some, for some reason this really cuts me deep down. When I was first getting to know my second cousin she'd always be asking to hang on the weekends. It was really awesome because we just "clicked".
She's had a pretty rough ride in life and since my sis & I came into her life she's been way happier. She's told me this and the fact that we are the only ones she hangs out with. She used to text every few days to a week and vice versa .
If I hadn't spoken to her for a week she'd wondered where I went/what happened. Only known her 8 months and over past 2 months she's acting distant towards me. I ask to catch up and she'll throw me the "I'm busy" line. I finally text her today explaining if I have been too full on and how she's gone distant and I understand if she doesn't want to carry on catching up. She explained life has gotten busy in general, and that it's got nothing to do with me being full on e.c.t
I understand what she's saying but at the same time I'm confused. The irony is that when we were first hanging out it was so full on (in a good way) she was afraid it would fizzle out because if this. We'll she's the one making it this way. I'm confused and just hurt. She hasn't had this much joy in a long time yet decides to spend most days on the weekends at her father's and she'd usually just do chores or errands. I believe if she really meant what she said, she'd make time and make more of an effort. It's obvious she doesn't miss me/us at all and I really miss her. I'm very busy too but I would make the time. People make an effort when it comes to a relationship because the significant other makes them happy e.c.t
How's this any different...I feel she only used me, and while she had no job in the beginning and such, she filled in her time with my sis & I.
Why was she so clingy and now she's so distant to the point where she can't even throw me a simple text.
No she isn't married. No she doesn't have a partner or a kid or a pet even.
Sorry this is long but needed to vent and no nasty comments please. I'll dismiss them