The "official" street gazetteer has Gambia Street running all the way up to Chancel Street, though it could be out of date.  https://www.findmystreet.co.uk/map?usrn=22501022

Perhaps the best way is to add in "Gambia Street Garden" as a public park and rename it to Marion's Way?   As long as there are objects with both names, people won't get lost.