Are you bfeeding? Breast milk squirted up the nose can help clear snottiness, and it has an anti-bacterial action. If not, you can get saline solutions to do the same thing. She probably won't like it much, but it will help. I also used to put some Olbas oil on the tissue and put it under the cot mattress to help her breathing.
Otherwise, lots of milk to keep her hydrated, lots of TLC and let everything else go hang while you cuddle your baby and make her feel better that way If she's sleeping on you, you can keep her more propped up to help the mucus drain.
Put something under the legs of her cot to raise the head end up. As suggested above, karvol is a good brand of olbas oil. Put some on a tissue near her head when feeding as well to help her breathe. As well as near her when asleep.
I just wipe the snot away with a baby wipe, never squirted anaything up nose!
My 3 month old DD has a cold at the minute too...caught it off me, unfortunately
We have put a rolled up towel under her cot mattress to elevate her head a little and put Karvol on a bib and hung it on the cot (well out of her reach). I've also got a bowl of water with a few drops of olbas oil sitting on the liing room radiator.
The first night DD came down with it, she woke herself up in distress because she was struggling to breathe. I took her into the bathroom and ran the shower to fill the room with steam. It eased her breathing enough for her to fall asleep on me.
She seems quite comfy in her bouncy chair because she's a bit more upright.
I haven't found the nasal suction thing any use at all and I'm not convinced as to the effectiveness of the saline nasal spray either.