There is a thread in Tips And Tricks called "Adding Harmonies" that talks about this..

http://www.pgmusic.com/forums/ubbthreads.php?ubb=showflat&Number=199488#Post199488


down in the thread a bit, is this (typical) explanation...

(It was a response in yet another thread that I reposted there)

"The BAIBettes - How I typically create harmonies"

(response to Jo's questions)
I can tell you what I do... though "your mileage may vary" (since I'm starting with a male vocal and you would be starting with a female vocal).

After getting the song set up in BIAB (meaning simply, the chords right), I open RealBand and load the BIAB file. Then import the vocal track. Select that vocal track, right-click and choose "Generate Audio Harmony (using PowerTracks or BBW...)"

I choose "Harmonize to the chord symbols of the song" - which is what the BIAB file is for. So far, I've only used "1 Down and 3 Up" as the type. And then generate. I don't typically change any of the settings in the plug in.

I then save each of the 4 (mono) tracks so that I can work with them in a different DAW (the one I know from the past). But you could simply work with them in RealBand

Listening to any one of the "voices" separately you will find... they don't sound "real". But add them all together at the right levels and you can get some decent results. But... not all the time. I often have to really lower or eliminate the highest one (because she's warbling something awful). Particularly if I am singing high (and loud). They (the BIABettes, as I called them) work best when I am singing low and soft - almost my natural speaking voice. At times, I have to drop them all out because they don't work for a particular phrase. A lot of it becomes finding where they work and how they fit in the song. And they work best (for me) when they are blended together. Here and there I will use the 1 Down and the first above - but most of the time it's all 4 together.

I pan two left and two right one a bit more than the other - meaning - L 70% L 50% R 50% R 70% (percentages out of 100). Obvious, I know, but some might not consider it...

150+ Songs produced using BIAB RealTracks
And 50 more...
and some more...