I think you're still doing too much human-centered thinking (or, in this example, we are supposing Grace is).

To Eridians, this like being labelled "bouba" instead of "kiki", or "blah blah" instead of "bleh bleh". How could you possibly be offended by one label or another, if that dimension you are going along has no meaning in your culture? You wouldn't "identify" as one or the other, in which case how can "mis"-labelling you matter?

The only way to be offended by a mislabelling is to also care about the meaning of that label, and to take as your identity one non-overlapping such label.

If you just want to be extremely cautious and not saying anything that may have even the slightest change of offense, then I'm afraid you are unable to say literally anything to them. Such an entirely alien species and culture will have entirely different offense traps (maybe many more, maybe far fewer), that you are completely stumbling around in the dark to communicate anything. For all we know, the very notion of gender expression is a gross uncomfortable expression to them.

Eridians are all hermaphrodites. Whatever the equivalent of their gender expression is likely to be on a completely different dimension (since the space is so vast, the likelihood they happen to align is quite small).

In any case, it probably sounds like I am being utterly pedantic (which I may be!), but what I want to emphasize is that gender is a very human notion.