Step 1: When she tires to speak in Japanese and messes up. Don't just laugh, text your friends what she said so they can laugh too.
Step 2: When she goes out stare at her like she is the devil incarnate which I'm 80% sure you think she is. Bonus points for little kids staring at her open mouthed and hiding when she turns and looks.
Step 3: Say the words `oki` and `sagaaru` often enough that the first words she learns by immersion are `big` and `tall`.
Step 4: Ask her why she came to Japan and when she says to learn Japanese, without missing a beat ask if she likes Japanese men.
Step 5: Don't carry shoes in her size. Make her buy mens shoes to emphasize her huge feet.
Step 6: Come up behind her and run your hands through her hair or randomly reach over and touch her hair while in the middle of a conversation.
But also be kind and welcoming. Check up on her to see how she is doing and be willing to teach and help her with anything she needs.