I'm a bit late, but here's another idea: take the Victoria line south
from H&I to KX, then catch the NR train from there. More walking, but
fewer stairs.

Yes, thanks. Offered that to her on the basis as there'd be no
additional cost[1] albeit takes ~10 minutes longer.


[1] like me is of the Freedom Pass generation - and determined to make
use of it before the 2015 Election decides we are wealthy pensioners
like Paul McCartney who don't need ......... If only!
--
Robin
reply to address is (meant to be) valid