Philippa is lovely! Vintage-chic, a bit clunky but in a charming way. Bold and strong, but also elegant and classy at the same time. As a horse lover I love the meaning. I think first of Pippa Middleton and then of Philippa Gregory (though I've never read anything by her), but to me those aren't bad associations. Philippa Marie is pretty and I like the significance it has for you.
I like Philippa Marie... it flows nicely. However, I've promised myself I'll never use Marie, Elizabeth, or Grace because they are the most common middle names. It kills me though because I LOVE MARIE & GRACE! I can see why those are used as middle names constantly... they flow with almost every first name you can think of.
@-bonfireazalea: thank you!
@babyprodigy- If Marie did not have meaning I so wouldn't use it but its a part of me I would love to be able to give to my future daughter.
If would be helpful to know more about your style...? Since we only have one name to go off of its hard to tell. Ill take another stab at it....