Sarah wants to, or has Andrew given her a deadline? If they're 'bestest' (her word) friends as she claims and the house is huge and can easily accommodate them both then why the need for her to move out at all? Much as I'm not much of an Andrew fan, he's been a very patient and forgiving gentleman towards his ex wife.
Hopefully he'd set up some sort of trust for her if necessary and leave the lion's share of his assets to their daughters, otherwise I fear Sarah would spend every cent leaving nothing for the girls from their father.
Who actually paid for the $50,000 Windsor birthday/charity anniversary dinner - Andrew (as some reported) or the Charity - might give us a hint as to his true feelings towards her.