I'm not sure if LMK view is quite correct. In a normal relationship then of course both partners would take their partners needs into consideration. BUT is a Ds relationshiop the same. If it is what is it that makes a Ds relationship Ds?

I would suggest the difference is the Dom does what pleases him and the sub derives her pleasure from the pleasure she gives to her dominant. He should not need to consider her, his pleasure is her pleasure.

This works when the couple are compatible, when their interests are broadly the same. In the OP case it seems Sirs Goodgirl wants to explore and either her partner doesn't want to or doesn't have the experience to offer her something new and different. Its blind lead blind. If her dominant didn't object to her being used by another be it a threesome, watching or loaning her out then compatibility is achieved.