Cat is missing...

I am starting to get worried.

We adopted two little strays whos mother abandoned them, Charli and LaBelle. We had Charli spayed this week and have been keeping her inside rather than outside like usual, but even so LaBelle was still around and being normal. Well sometime yesterday evening she wasn't around and she never did come last night when we called/tried to feed her and she wasn't in the cathouse or the shed. This morning she wasn't outside waiting for my mom to go to work like she is every morning. And when I just tried to call her and feed her she never came.

Is it possible she went of "looking" for her sister who is inside recouping?

Its possible, but why is the other not spayed too? She could also be checking out the local tom cats and will come home after being bred.

We couldn't afford to do them both at the same time/keep them both in at the same time. We were planning on getting her done next week. Charli was experiencing signs of heat so we went ahead to get her spayed, but LaBelle was not and was rather lazy laying around and wanting attention etc, and she's never done this before.

Lazy and wanting attention sounds like she was on her way into heat. Too bad you couldn't manage to keep both inside.