So, we moved in the last few months to a new house. A couple of months after we moved in, while it was still nice enough to sit outside in the evening, we started to be visited by a very cute cat. We fed her a few BBQ scraps, and she was only an occasional visitor.
When it got a bit too cold for outside, she'd turn up at our back door about once a week or so, I actually bought some cat food for if she called again.
Recently she has been showing up every day wanting feeding, and literally tries to dive in through the back door the second I open it when I get in from work. This is annoying because I smoke, and usually want one once I'm home

One day I left the very top half-window a fraction open as I wanted a cig but didn't feel like opening the door to her...she must have gone through an amazing series of leaps and bounds, but she got through it and landed in my kitchen sink!
How do I know if she is just greedy and does actually belong to someone? She wears no collar, and when I feed her, she seems absolutely ravenous. She's not fat, she's not skinny...
I'm asking really not just because it's annoying, and if I wanted the encumbrance of a pet, I'd get one, but because I'm going on holiday next week for 2 1/2 weeks and I'm fretting about whether she'll be ok if I'm not there to help her out if she needs it
Can someone that understands cats a little better than I help please?