The pdsa are imho amazing and are very thorough,it's unfortunate that you had an uncomfortable account with the vet in question,but if she/he doesn't think theirs a problem-the chances are their isn't,however if you are still worried then yes get a 2nd opinion but if she is well in herself apart from the obvious traits of pregnancy then this is a good sign as from my own experience if you have an unwell cat they do find a way to tell you and are perstistant til you get it-so at this time i really wouldn't worry to much,just continue observing her