J.,
this sounds very difficult on a lot of levels. There are a lot of safe and natural herbal products and homeopathic products made for little ones your baby's age that will promote a more restful night's sleep. You can give it to her before bed.Chamomile, either as a tea, a homeopathic or a tincture is my herb of choice. It is very safe and also helps with teething. There are other homeopathic blended products made just for kids, e.g. Calm Forte. There is also Chamocalm (or something like that) made by Herbs for Kids--it is made with glycerin so kids love the taste.
You may want to check out Flower Essences, too. They are very mild, a vibrational therapy that works very subtly, and there are ones for nightmares. I have used Flower Essences (The brands are Flower Essence Society-FES or Bach makes a very nice "nighttime rescue" formula that promotes restful sleep but I don't know if it would work on nightmares, I suspect it would) very successfully with my 2-year old throughout his babydom to alleviate disorders such as separation anxiety and for weaning. Flower essences work to restore emotional balance. I love the regular Rescue Remedy for accidents and emotional trauma any time of the day. You could take it too, while this is happening, to give you extra perspective and emotional support. 4 drops every 15 mins until you feel better!
Finally, I would talk to your daughter every night before sleep. Tell her how much you love sleeping and how restful and restorative it is. Talk to her about dreaming and help her "program" herself to have dreams that are filled with the images, experiences, people and things she loves. Reind her that she always has the choice to change her dream to something she likes, or she can wake up and ask for cuddles if she doesn't like a dream. If she wakes up from a dream, ask her what she was dreaming about. At 18months she probably won't be able to tell you, but it starts laying the ground for when she WILL be able to tell you in another 4-10 months.
Let me know if you try anything and if it works.
Best of luck,
S.