I'm with you 100%! I hope you can gently persuade your sister to try something else. If she won't listen to you, I'm sure she won't be interested in the opinion of some unknown nurse and mom thousands of miles away, but I'm good at wasting my breath, so here goes:
IMHO, the Playtex Nurser is the WORST infant feeding product available today (followed by the disposable NUK nipples provided to hospitals), but I digress. The nipples are very firm, short and stubby, and are difficult for ANY baby to latch on to, let alone an infant who is used to nursing on mother's softer, longer and more pliable breast. Suggest to her that she breastfeed exclusively for 3 weeks or so to establish a good milk supply. Hopefully by then her baby will be so used to his mother's breast that he will reject the Playtex nipple. She can then try a standard nipple or a comercially available NUK.
Is she attracted to the Playtex system because of the ease of pumping, storing and bottle-feeding her milk? If so, there are other systems available that are just as convenient, and a lot more baby-friendly. Take her shopping!
Good luck, and happy birthing to your sister!