Echo what betty said. I am a foster carer for a ten year old and I would initially be very wary of any relationship she was in - nothing to do with you and your ds but to do with how she had been brought up and the reasons she came into care.
My ten year old came to me with a ton of make-up, playboy stuff, high heels, hair straighteners and some very sexually precocious behaviour (as had suffered abuse)so if she came as a teen and had this behaviour been much much more then I, in turn, would have been much more wary.
It's a fab idea to introduce yourself to their carers - be really upfront in private with them about it not being a sexual relationship as they will probably just have come from their 'safe caring' course and will be worried about all sorts of stuff.
Good luck and how great you are to think of this.
She will need the continuity of her boyfriend to cope with the transition probably