The other thing is that you are likely making her feel inadequate by being seen beside you. Gently tell her that rather than dragging you down, she should use the opportunity to pick up her own game too. Take her out shopping and buy her some nice clothes. Get her out of jeans/t-shirts and encourage her to wear nice dresses, and skirts. Make sure she wears them when you both dress up to go out to a nice restaurant, the opera, or a jazz club. That usually patches things up.Maybe your girlfriend is insecure about her own style or appearance and is consciously/subconsciously afraid that if you suddenly go through an "extreme makeover", you might also decide to makeover your relationship choice...
I have encouraged my partner to take up sewing, and brought her a sewing machine for Christmas. I have even figured out how to draft a pattern for a basic tailored skirt. I am going next draft a multi-gored skirt using the two panel tailored skirt pattern as the basis. The muslin fit for the tailored skirt looked very good too, although I had to systematically point out to her how a bespoke pattern was a dramatic improvement over the RTW skirts she had in her closet.
I use a 1942 text by Harriet Peppin to draft (I'm sure TheWardrobeGirl knows the book) to draft. I had to slowly convince her that the skirt waistband should sit on the natural waistline and that the tight fitting and dead straight pencil silhouette skirts currently fashionable aren't actually slimming, and it was better to have a bit of an A-line to make the waist look narrow compared to the hem. That's how Lucille Ball wears her skirts and l love the look.