I am glad you have a capable friend that is willing to have a feel of Sox's tummy to try and feel for kittens. I am also happy to hear that after this litter you are planning on spaying her
, it is for the best all round as I am sure your friend has already emphasised no end. Do you know if Sox got out on her third day of her season (calling)? Because if she got out prior to the third day there is still a chance she wont be pregnent. For your sake I hope Sox only has a small litter, hopefully that way it will be easier to rehome any kittens if you choice to or can't keep them yourself. A handy tip from a vet is that if Sox starts calling again in 3 weeks (from the time she first got out) then its a pretty sure bet that she isn't pregnant.
If Sox is pregnant and when she does go into labour keep an eye on her but don't go bugging her. By keeping an eye on her during the labour you will be more aware if she has developed any complications and be able to get her to a vet quickly with less danger to her and the unborn kittens lives. I am not saying she will have problems but best to be on the safe side.
And now some other useful info...
If your planning on worming Sox do it around the middle of her pregnancy as in the first 3 weeks you run the risk of baby deformity and in the last 3 weeks the risk of abortion or premmi kittens.
When it comes time for Sox to give birth the first clues for you will be that she is fairly restless, and spends more time in her chosen 'nest/ den' and refuses to eat. Generally speaking the intervals between kittens is anything from 20minutes to 2 hours, if it takes any longer than this its time for a visit to the vet.
Hope some of this very basic info helps and that you have a pleasant uneventful time with Sox and her expected kittens, also be sure to talk to a vet about any concerns you have in regards to extra vitamin and mineral supplements for Sox along with any medications.
Good luck