I hear ya!! I have two sick kiddos, although they are 4 yrs and 2yrs. My 2 yr old has pneumonia (at emerg on Christmas Eve) and the 4 yr old has bronchitis. It has been a lovely holiday in our house

!!!
I know when my girls were babies and would get that congestion I always put a couple of folded towels, fairly flat, but just a little lift and I put them under one end of the mattress. It wasn't noticeable to look at, but it gave the mattress a bit of a lift so that they weren't totally laying flat. It always seemed to help them sleep better in that they could clear some of that mucous.
I also use a cool mist vapourizer. I have always used one since I was a kid and this is recommended more than the warm mist (for bacteria growth).
I also use the stuff that Johnson and Johnson has out that you rub on their chests (like a baby version of Vapo rub ... which you CAN'T use!!). They kind of smell like a little basted turkey!! It is a ecalyptus (?) I think!
A bath in a warm bathroom is soothing because the steam will loosen up the mucous so it "comes out!". If you don't want to do a bath, stand in the bathroom with the shower on high and it steams up pretty quick. This used to help my girls breathe a little easier after about 2 or 3 minutes!
I hope she feels better

There is nothing worse than a sick little one. They just don't know what to do with themselves. Our youngest had RSV while we were in Florida when she was 7 months old. It was so hard because I had never seen her so sick. She was absolutely lethargic. It breaks your heart
Good luck ...
Kerri
p.s. Oh ... and before we had an actual RSV diagnosis while on holiday, we were using some great saline drops for infants, and then suctionning her nose. They were awesome ... but I don't remember the name of them!!! The pharmacist recommended them and it was the BEST thing to get rid of the mucous. They were the drops, not the spray ... it may have been pedia care, but I don't really think so. I know there was an infant one and a child version. This REALLY works ... I had to do it with an adult version when I had a sinus infection and it really did help me to breathe!!