PRS vs PPL vs Soundreef etc - confused

Hi,
I'd really appreciate some advice thanks as I'm new to all this music lisencimg stuff.
My friend wrote a melody and lyrics and I added all the instrumentation and production.
Spotify has had some listens (73k) surprisingly and BBC introducing have listened and a radio station wants to play it.
We agreed a split for any futures royalties and I said I'd look into it.
One hour later on Google and I'm very confused haha. PRS PPL etc etc.
Does she join only or I do too?
How does these companies know what the agreed split it anyway?
She is only 16 so do I join as a publisher and add her (and me?) as an artist / producer / musician.
Thanks very much!
Gavin
I'd really appreciate some advice thanks as I'm new to all this music lisencimg stuff.
My friend wrote a melody and lyrics and I added all the instrumentation and production.
Spotify has had some listens (73k) surprisingly and BBC introducing have listened and a radio station wants to play it.
We agreed a split for any futures royalties and I said I'd look into it.
One hour later on Google and I'm very confused haha. PRS PPL etc etc.
Does she join only or I do too?
How does these companies know what the agreed split it anyway?
She is only 16 so do I join as a publisher and add her (and me?) as an artist / producer / musician.
Thanks very much!
Gavin