Well yes some people have but some people havent depends on the position they are lying in - my friend couldnt hear hers at 13 weeks and because the doctor couldnt find it she gave her a refferral for an u/s saying threatened misscarrage (imagine the night she had worrying) so when she got to the scan and there was nothing the matter with the baby he was fine it all depends but some have...
I first heard mine at 15 weeks.
Get her to try and if you cant find it ask her to use the portable ultrasound machine so you have some reassurance...When I was 16 weeks I think we couldnt find it once and was because baby was behind my bladder so we used the portable ultrasound she was fine, so we put the doppler back on and we heard it! they are smart little things you know!!!
Have fun!