First of all, Bless You, for helping her out like that. The real reward for doing stuff like that is yet to come, but, you may have to wait quite a while for that.
Secondly, I'm really confused by the process you've described there !
I may not be "seeing" apples to apples here, since I've got Comcast Dig Preferred, via their Scientific Atlanta 3250HD Box.
I also have a separate line for my OTA, which I access via the sources in my HDTV.
One can not receive HD, with a direct connection of the Comcast Cable into the "F" connector of their TV, even if it's an HDTV. Those lower channels (2-99) are still NTSC/Analog. Even with the Basic Service, one must have one of their Boxes, to receive HD, and even with Basic, they provide a "few" HD channels.
The inconsistency is what's confusing. I've tuned in Digital on a Comcast direct connection, but, I was using a Samsung H260F D/A Tuner. That gives you the 75.1 to 135.### channels, and you receive what's not scrambled. Very few by the way.
Does her new TV have all three tuners ? NTSC/Analog, ATSC/Digital and QAM ?
I think I can say this for sure...
IF you want her to see reliable HD via Comcast, you're going to have to get her to rent one of their Boxes.
With that, the HD that Comcast provides, is VASTLY inferior to what she could receive, IF she were to get an OTA Antenna. Depending on where she lives, probably a Set Top Indoor may work.
I guarantee you, when she sees OTA HD, she'll be sorry she's paying for what Comcast delivers !
I have my OTA Antenna Coax, connected into the Antenna "F" connector, and am using A/V (component) for the CBox.
I'm not sure at this point, if I've actually answered any of your questions !
But I have a couple...
Does she now have an OTA Antena outide or inside ?
Is she renting one of the Comcast Boxs ?
Have a good Day !