IR stands for Infra Red which requires you stay in the same room. I believe the headphones have to be able to see the transmitting unit. RF stands for Radio Frequency and supposedly you're able to leave the room and the headphones still work. I've tried a couple of wireless headsets and haven't been too happy with them. Right now, I'm using an AR 900Mhz RF unit. My biggest complaint with the two I've had, is that the tuning control on the headsets are very touchy. Try to fine tune just a little bit and you lose the signal.

Actually, I just happen to have the same DVD recorder/player (under the Costco model number) in one of our rooms. So, I just double checked and confirmed that the analog R/L audio is still available when using the HDMI output. The audio OUTPUT is the second set of of red/white connectors when viewing the back of the DVD player (from left to right). Make sure you have the proper connection. Again though, does your television have line level audio output connections? Do you have the make/model number of the television?

What brand are your headphones?

Sennheiser is very good quality, some pros use them on stage as well, for mics and their instruments. It would be good if you could borrow the different sets and see if she likes them to hear and is comfortable. Wireless equipment can be battery hogs, so consider this point.