Why did the McCanns really get rid of Justine McGuinness?

This was raised on Twitter tonight. We were told at the time that Gerry had a falling out with Justine McGuinness, over her expenses claims and that's why they parted company. Was that the real reason, though?

1. Did the McCanns (or any other connected party) realise that this was all getting too big and out of hand, and that Justine wasn't up to the job?
2. Or did they feel they couldn't trust her to keep her mouth shut?
3. Or was the sacking of Justine an excuse to draft in Clarrie? And why?

I don't for one nanosecond believe the tales that Justine charged too much, because Clarrie is a lot more expensive to keep. No, either Justine was a potential liability and had to be got rid of, or Clarence had to be drafted in for some reason that we don't know about.