First off...
Welcome to the Planet....
second...
If I were the butch in question, I would be thrilled to have you show up in you corset and stockings. It sounds like she is in to you, and if you have already had sex, then it would be completely appropriate to have a little "surprise" for her to show your appreciation...
if she is a sweet and attentive as you described, and has openly expressed an interest in sexy lingerie, then you need not worry about any awkward moments...
as far as the age and gravity, full figured mature women are HOTTTT!!!!!
so put on your sexy gear and RAGE ON SISTER!!!!