@seedybird she should not need any top up. Rent covered by loan with £5.5k to live on is more than any students I know. As long as she does not have an expensive commute she should be fine.
Most people say rent plus minimum loan £4k, which is just over £100/week in term time, is adequate. The reason London students get more is mainly because of the high rent. Of course you will probably want to get the of shop for her and may want to continue to cover her mobile phone, but she really should be fine.