I'm a little baffled that your doctor gave your 5 mos. old dimetapp dm. Those were taken off the market for children under 6 years of age. Also, I remember being told that a baby shouldn't drink any herbs because of possible allergic reaction, however, I just read this article from iVillage regarding its use and they say differently: http://parenting.ivillage.com/newborn/nhealth/0,,3qkb,00.....
Perhaps, you already have, but if not, maybe some additional thorough research in that area would be a good idea.
Now, on to your actual question of what else you can do;) Humidifier and saline nasal spray are effective, safe and most often recommended I have found to help ease the discomfort of a sick baby. Since you can't use Vicks Baby on a baby so young, you may want to get some vicks and put it in one of those candle/room diffuser thingies to help her breathe. They also have the ones you can plug into the wall. Also a nice steamy bathroom and lukewarm bath with just a bit of lavender and tea tree essential oil in the water may help. Speaking of the diffuser, when my son was sick, I would often mix some lavender and tea tree oil with a little water and put it in the diffuser. Both oils have antiseptic properties, will make the room smell nice and will help your baby breathe a bit better.
As with all colds, it's just a waiting game and as difficult as it is to watch your baby struggle like that, know that you're doing everything you can and your comfort is helping.
p.s., I have read it over and over again (see Baby 411) that if your baby has a fever, that is good thing, it is their body working to fight off the infection so please don't give tylenol unless it's a really high fever (see Baby 411 to know what is considered a high fever your baby's age). Our son had a fever awhile back and we didn't give him tylenol, just kept checking his temperature. That same night, the fever broke and he was all better by morning.
Good luck!