Angels unlimited- fighting fit

This book is about an angel called Mel Beeby. Mel has a crush on an angel called Orlando but she knows that he doesn't even notice her so to take her mind of things she started going to the gym and concentrating extra hard in her school work. But then one day when going back to her dorm she runs into Orlando, he says for her to meet him in the library, at first she thought it was a date but when she gets there it turns out that he only asked her there to go with him and some other angels to Ancient Rome for a mission that was top secret. She was the only girl going and she had to learn how to dress and style her hair as a woman instead of learning to fight. When they arrive in Rome they pose as slaves, Mel gets bought along with her friend Reuben to a girl called Aurelia. Orlando tells her that she has to keep an eye on Aurelia, it turns out that Aurelia was sneaking around to meetings for Christians, in those days Christians were considered barbarians, when they are found out they get arrested and sent in a cage with lions but as Reuben and Mel were angles they spoke animal languages so the animals did not attack them Nero the emperor wanted to learn how to do it so he asks Reuben to teach him but he refuses and they get sent to jail but the locks were easy to open so they sneaked out. On the way to Orlando they see a Vestal Virgin, a very religious person, walk by that looked exactly like Aurelia but they ignored it and found Orlando, when they got to Orlando he was with one of the Gladiatrixs that turned out to be Aurelia's twin sister but then Orlando explains that they were only two of a set of triplets and that the vestal virgin, Lucilla, was one of the triplets that had been born upon a curse that said if the triplets were reunited the earth would fall but Orlando said that it was the complete opposite, they would make earth a better place. They find Lucilla and reunite her with Star and Aurelia but then Nero comes and stabs Star and she dies. But it doesn't matter because the sisters were reunited.