Exactly that's why. On the tour it was always just five members, but it was six girls for the show at Slane Castle. Therefore they partly gave away solo lines that actually belonged to one girl to another, so it would fit "space" wise. Chloe was usually in the center and so they thought it would fit to give her lines form the tour to Hayley who sang on tour the lines Méav did when she was not touring. Also, Hayley was not exactly "brand new", more of a special guest. I don't see why she should not get some pore parts, especially considering Chloe did not only have the most screen time in the original show and she appeared in all group numers in the ANJ dvd, which Hayley did not.
Chloe wasn't in all the group numbers at Slane. At the Ceili?
Orionco Flow?
Also, after she sung "The Prayer", she wasn't seen again until the second to last number of the first act (Over the Rainbow). And in Act 2, she didn't appear until the 4th number (Sing Out). And "Spanish Lady" is the only number that I recall where Chloe stood in the middle of all the girls. Also, Meav appeared in more numbers than Chloe in the original show.