Asthma doesn't render someone incapable of working. (Many professional sports players suffer from asthma). So that rules out any sort of invalidity benefit. Which basically only leaves Job Seeker's Allowance (and the benefits which can run alongside it).
http://www.direct.gov...ngforwork/DG_10018757
In order to qualify for JSA a person needs to be able to show that they're actively seeking work, and they must accept any reasonable work offer they receive. If your friend is receiving JSA (or is otherwise on a very low income) she might be eligible for Local Housing Allowance (but only on the basis of living in shared accommodation):
http://www.direct.gov...ow_income/DG_10018928
and Council Tax Benefit:
http://www.direct.gov...ow_income/DG_10018923
As your friend probably won't have the record of National Insurance contributions necessary to get Contribution-Based JSA, she'd receive Income-Based JSA. That would probably be better anyway, as she'd then be entitled to free NHS prescriptions.
Anyone (irrespective of their income levels or benefits received) who needs frequent NHS prescriptions can make a single payment of £28.25 to cover an unlimited number of prescriptions over a 3 month period (or £104.00 for a full year's cover):
01:34 Wed 05th Jan 2011