Fran
Do you mean Severe Disablement Allowance or the Severe Disability Premium?
The former is treated as a Contribution Based benefit which means that it is in the name of the claimant only, however, I've not dealt with this benefit as it was discontinued many years ago and there may be rules that I am not aware of.
If you mean the Premium then one of the rules is that the claimant lives alone or is considered to be living alone, however, you may have a bigger problem as the Premiums are only paid with Income Related benefits and a partner working full time will stop those benefits being paid.
I would put your joint information into one of the online benefit calculators to see how your benefits would be effected.
www.gov.uk/benefits-calculators Gordon