I don't know if the trust allows this, but why can't you take out an "immediate needs annuity" policy instead, by swapping a lump of Capital in the trust and purchasing a policy that guarantees to pay out for her longevity.
At the ripe old age of 100 the cost of the policy would surely reflect her shortened life expectancy....after all you would be acting in her better interests by safeguarding and securing her current residence. The policy would guarantee to pay the necessary nursing home fees until the end of her life. Link for information purposes below.
http://www.sharingpensions.co.uk/annuity_immediate_needs.htm