Authors have many reasons for changing the emphasis of their writing careers, and she should be given a full pass for admitting writing sex scenes just doesn't do it for her anymore (= they are difficult for her to write). This marks a change in her writing career that may not be well-accepted by some of her readers. It may even decrease her future sales. But she is entitled to write what she wants to write. Although several jokes have come to mind concerning sex and the elderly, I have to give her kudos for being upfront about her writing and about her personal life. Anyone who thinks personal challenges, including aging, don't impact one's writing should hold his/her breath and hope no major personal disasters are waiting around the corner.
And about that one comment, I would like to have seen her expression when she said it, and how her surrounding comments put it into her intended context. It comes off as stark in the isolated quote, which I agree, is unfortunate.