Alice had considerable property in her own right - she was heiress of her family, the Montagus or Montacutes or whatever you wish to spell them as. This may have been the reason for attainder, but then again the Countess of Warwick was substantially richer in her own right and she was not attainted. So maybe, just maybe, Alice was a political animal and really involved in Yorkist conspiracy. Or maybe Margaret of Anjou just plain didn't like her.
Unusually the attainders included a clause promising pardon for humble submission, and one is left wondering what would have happened if York and Co. had humbly submitted. The jointures of wives were protected and Duchess Cecily (or Cecille if you prefer her own version) who had no jointure received 1000 marks a year. This was relatively generous and certainly more so than similar arrangements in the Yorkist and Tudor eras.
The forfeited estates were not dismembered, but some parts of them were granted out on lease to various Lancastrian supporters. These included the Duke of Exeter, the Duchess of Somerset, the earls of Wiltshire and Pembroke, and Lords Dudley and Egremont. There was resistance to the forfeitures, particularly in the Welsh Marches where certain castles, including Denbigh (prop. R. York), were held against the Government forces.
Another good centre of resistance was York's town of Newbury. In June 1460 Wiltshire, with Lords Scales and Hungerford, visited in the role of justices of oyer and terminer in response to a revolt against taxation. Several local men were hanged while seventy-five others were imprisoned in Wallingford Castle.
This made for good propaganda, and Warwick (in particular) was just the man to use it.