Boy, what a complicated mess. I'll try to be succinct and clear with my thoughts:

She's moving to be with him in August (which seems like a pretty big deal)--and already calls herself his slave (which seems like a VERY big deal to me). Soooo:

Communication is never a bad thing.

Discussion of fears, expections, desires and emotional issues should, presumably, be happening considering the future arrangements set to take place (although it doesn't sound like it is)...so that might be a good place to start.

'Master said that there would be no sex with this other slave'...Recently? Is the picture a recent shot? Your friend seemed to feel that *something* was going on or she wouldn't have felt compelled to peek...trust may have already been an issue and now that's just been made an even larger issue.