This also sometimes happens to my 2 year-old - pretty gross, but it seems every time he is sick there is just a huge volume of mucus, and unless he has a massive sneeze, it just all drains down his throat. It's maddening because we aren't supposed to be giving cold medicines these days with all of the warnings, and my pediatrician has always been anti-cold medicine for babies anyway. I noticed a post below about giving Benadryl - they have even updated their own website to alert parents not to administer Benadryl to children under 4.
So what's worked wonders for us is the saline nose spray. I noticed 1 other post below mentions it. There are several brands - buy one that's made for kids so it's super gentle. There is Ocean for Kids and Little Noses. You spray it right into her nose (she probably won't love it, but it's better than vomiting!). It breaks down the mucus, making it thinner, and therefore easier for her to pass instead of it sitting in her stomach. Mucus is also super acidic, so a build-up of it does cause vomiting, and also diaper rashes for younger ones when passed in stool. The saline helps break it down and does wonders relieving both the vomiting and the diaper rashes.
Also we run a humidifier at night - regarding the one that you put medicine like Vick's into - that isn't recommended for kids her age. We have one made by Vick's but just run it with water in it, we don't use the medicine. Also sleeping on a pillow so her head is elevated can help too.
Best of luck, and those warm months can't come soon enough!