OK deep breath
along trhe top of your screen is a row of buttons just above where the posts come up..............the first one says home.
Click on that and you see every board that we have.
You will find one called Cat heath and behavior and thats probably the one you want right now
When you have time pop into all the boards just to get a flavour of what they are all about.
Right at the very top on the left under the Purrs banner and next to your name it says All unread posts.............click on that and you will see all the threads you havent read with the newest at the top
Now about your cats...........they will have picked up a feeling from your cat hating friend and so will probably stay out of her way until she has gone ........cats are clever
Of there is another cat coming in your house, then he could be , most likely to be upsetting your cats and the diareaha could be from yours or him. Somehow you need to stop him coming in if possible, does your flap lock?
Do you know who owns him cos it may be best to have a word with them if possible.