Realizing a relationship isn't as important to the other person as it is to you can be painful, and Greta could be hurt not to receive an invitation. Being excluded sucks, and being excluded from a major life event by somebody you consider almost-family sucks worse! But LW needs to realize this is between Riley and Greta, and she has no information beyond rumors. I think LW can have one short conversation with Riley to say Greta has always treated her like family and would love to receive an invitation, but then she needs to drop it.