Just found your post - a bit late to go outside and have a closer look, but after quite a lot of digging (figuratively speaking) I'd say it's a variety of Veronica longifolia (related to the little blue speedwells you find everywhere, including in your lawn). 99.9% sure. Have a look on Google images, click on pink varieties as the veronicas are mostly blue. A hardy perennial, looks as if it might take the place over if you don't threaten it with a spade now and then. I'm a gardener by trade, trust me