I agree with all that's been said. One additional factor to keep in mind.......people buy freeholds in order to make a profit and they are entitled to make a return on their investment.
If all the charges are legitimate then £500 management charge is incredibly low. Just think about it......paper, postage, telephone, printer ink, time, effort, travel etc.
The total charges equate to £710 per flat or £59 per month. Some of my flats are £1200-£1500 pa
You have no reserve funds for emergency repairs or external redecorating. What about buildings insurance ?
.......and you cannot expect to be provided with the receipts and invoices. You are only entitled to view them but not to have them sent to you or for you to take them away. She will be entitled to charge you for copies etc.