I find it less offensive than unfortunate--it perpetuates the stereotype of the male-bodied female-presenting (sort of, here) person as a figure to be laughed at, as a figure that is not meant to represent likely or non-comedic reality. This is the way cross-dressing male-bodied persons have been portrayed in films and television shows for ages. Sure, Sun Mum is gendered as "she," but "she" makes no effort at actually presenting as female, and I assume we are not meant to assume Sun Mum is *actually* female, like a transwoman would be, so the "she" gendering here actually bothers me a bit because it seems like just more comedy to me rather than accuracy of gendering.
There's much worse out there, which is why this seems tame to me, but I don't find the female gendering at the end a real positive and the ad as a whole is a rehash of the trope of the to-be-laughed-at ->-bleeped-<- male.