Hi Colleen @colleenyoung, I'm a mouth breather also and I was a little apprehensive at first. I think having a mask that is comfortable is key. I got my CPAP last July and have been through 4 different types of full face masks. My sleep medicine doc told me if I had trouble at first to just wear it an hour or so watching TV to get used to how it feels. I went cold turkey though and didn't have too much trouble. One problem I had was the hose getting in the way (I toss and turn a little during the night). I found a hose stand that holds it up above your head that works fairly well. You can put the stand under the mattress at the top of the bed or on the floor next to the bed to keep the hose above the head.

@colleenyoung- As a C-pap userfor over 20 years I can offer a few things to you Colleen. John is right about the fit of the mask. I too am a mouth breather and consequently was recommended a full face mask. I tried a half a dozen of them and could not find one that was a good fit. It was determined I have a "tweener" shaped face which simpley meant I was in between sizes? I didn't really like them anyway due to the somewhat claustrophobic feeling I got using them. I went to a nasal mask that with a chin strap was just right for me.
Chin straps are a bit of a pain, but once you find the right one that does not slip off your head in the middle of the night the results of a dry mouth and higher AHI scores go away. I wish you all the best in helping your mom with this device. Once she gets 7+ hrs. of sleep with good equipement she will wake up so refressed once again! Happy Zzzz's! Jim @thankful