It's unlikely you will feel anything at the stage or anyway - please don't palpate her, it needs an experienced person to do it.

I suggest you take her to the vets, explain about her escaping during her season and get a mismate injection and then get her spayed, preferably mid way between season. Many vets don't like terminating pregnancies, however, this poor bitch is on her second home already, is already a cross and you have no idea what the father is if she is pregnant, and in this climate it would be hugely irresponsible to go ahead with a litter.

An in season bitch should not be allowed into the garden unsupervised - not only would she not have had the opportunity to escape, but she will also attract dogs and you may find one has got into your garden too.

Please check your fences - to escape once is possible, but to have done it on several occasions is.... well........... I won't say, but I think you get the gist.