Hi H.,
My 4.5 year old was the same way. I feel for you! My son was walking on his own at 14 months. I think that the rough patch has to do with the development that goes on in the brain between the crawling and walking stage. Once my son was fully walking on his own, the sleep patterns changed 100%. I FINALLY got at least 6 hours of uninterrupted sleep each night.
I would recommend the usual: make your bedtime routine really solid - same time, same place, same rituals (warm bath, PJs, books/singing). No TV. Nothing overly stimulating. If she has a security object (blanket, doll, etc.) put her to bed with that - or something that smells like you (a T-shirt, etc.)
Make sure she is getting her two solid naps each day. The napping during the day will save you at night.
Also make sure that you walk her around a ton during the day (or have her walk). She will be a little more physically exhausted for you, and she will also be pushing to carry out the last of that brain development that goes on with the walking stage.
IT WILL GET BETTER. My husband used to have to drive my son from Portland to Tillamook early each morning...just so I could get a couple of hours of uninterrupted sleep. It was a nightmare, but it does get better. Some children are just born with highly reactive neurological systems. They're smart cookies, but it's SO hard on the parents. Hang in there.