ok, it is a small machine, about the size of a flat vanity case (if that makes sense). the tubing is quite long, and can get tangled up if i am not careful, but i am so used to it now that even in my sleep i unwrap myself from it!
Most newer machines come with an inbuilt humidifier (and i would def check if your DD's is) as that stops the dry throat that some CPAP machines can cause.
The machine is callibrated to your own pressure needs, and mine has timer buttons on the top, 5 mins, 10 mins, 15 mins and 20 mins, as well as a 'on' switch. What this means is that instead of going to full pressure straight away, which can kind of take your breath away as you struggle to get used to it (which can be quite frightening for little ones - my DD1 used to love having a go on it!), you can set it so that it will gradually increase up to full pressure.
Once i got used to it (2-3 weeks) i found it quite easy to sleep with it - and i am a very restless sleeper! The trick is to make sure that head straps are adjusted properly, which ensures that the mask part doesnt move, which can lead to offshoots of air under the eyes, which is annoying! Oh, and my mask (but it is quite an older style so newer ones might not have this) has a big air escape from the bottom of the mast (intentional), and when DD2 is in bed with me, i have to be careful with her, as it can be like lying right next to a huge draft lol!
it can be tricky to get right, but once it is, it is well worth the effort, and hopefully your DD2 will feel the benefits!
Oh, and i have travelled abroad with it, needed a letter from the consultant, and had to take it on as hand luggage. Nights in hospital etc are fine as well, though some are more accomodatiing than others - some insist on it being checked out by their electricians etc.
I hope i didnt waffle on too much, and was of some use!