<human>: Summarize the given text in a few sentences.

My cat is a year old as of last month. She is/was in the waiting line to be spayed by the local humane society as they do cheap spays and shots for those who meet certain criteria, because I am a college student I can take advantage of this program but the only draw back is a month or more waiting period, and so I've been waiting for her number to be called but it hasn't yet. This is her second time going into heat.

The issue at hand, my cat is not an outdoor cat but we do let her on our roof, it can be accessed from the windows and there is no way down or up, or so we thought, and that is the only reason she has any outdoor time. Well yesterday morning I woke up to my cat coming back through my window and going out my bedroom door, when I looked up there was a second cat standing at the foot of my bed, a neighborhood stray I hadn't seen before. I was startled and the cat took off out my window and down a tree that is on the side of my house, that I didn't think was close enough to use as a way up or down. I checked my cat for bites and she was missing some fur on the side of her neck, but no open wounds, and has been walking around with her tail down and grooming her genital area a lot more than usual. 

My questions would be how soon can I tell if she is pregnant and what to do if she is as far as any necessary food changes, vitamins, space for birthing, etc. I've had cats all my life but usually males and only dealt with new born kittens once a long time ago when I was 4-5.
<bot>: unspayed cat got out and was probably mated with by a stray, what do I need to do to help if she is pregnant?