if she is 10 days late she should take a home pregnancy test. If she was 10 days late, but then her period came (a regular period not just spotting) then it's unlikely that she is pregnant.
Was her period normal the month she had it? If so, easiest suggestion is for her to do HPT and that way you will get an answer one way or another. If she was stressing about the possibility of becoming pregnant than that stress could have delayed her period.