Bookkeeping on Macs

I have a client who is a psychotherapist, working out of her home. She is extremely disorganized, so needs a lot of support!

Currently, she has no accounting or bookkeeping system at all (I'm not sure what her accountant thinks of her at tax time!). She has asked me to set up a simple system. Ordinarily I would just suggest QuickBooks, which is what I've always used, but she has a Mac - and QuickBooks for Macs seems to be far more expensive than the PC version.

Does anyone have any suggestions for a good, basic, simple accounting software that she could use?

So far, she is not a "virtual" client, as I go to her office/home. Eventually this may change - is any software transferable back and forth from Mac to PC?

Thanks for any suggestions!