swaddle and put a rolled up blanket behind them.

oh please be careful with putting her in anything that makes her cradle up. i understand your struggle but she should sleep flat. car seats and swings are not sleep safe. you could try putting. towel under the head of her mattress. not to high just slightly but in a way that keeps it firm. and not on top where she sinks into it. may take a few tries to get it the right fold. Oh i once used a 3 ring hard binder for something like that. it is wedge shaped and you can mke sure it is hard. i hope that helps and i pray she feels better soon.

my daughter slept on my chest every day she was sick it's tiring but that was the only way she could breath good

put her in her swing to sleep or rocker