Those are perfection. I had a similar issue with a lady friend .
The remedy was a little toe sucking/nibbling, with a tongue slipped between her toes. She found it , fun,amusing, it tickled like hell but not unbearably so. She laughed her head off and enjoyed it . That act alone brokered the tickling deal for the future. It built up.the trust and removed the fear.
Hope that helps pal. Good luck