It doesn't roll off the tongue easily for me it's not an issue of it being a vowel though to me because example Marlow Elaine flows fine to be. I just think they both are a bit harsher of names so combined it's not great. Etta in general is hard in the middle I think.
Off topic: Is the E on the end on purpose? And personally- people aren't going to be calling her Marlow Etta Proudly all her life and mashing them together. So if you like it, go for it.
It's fine. Not like Lucy Mae where you might use the middle name routinely. The only time we usually use middle names is when someone's in a lot of trouble or when Comcast customer service is being dicks and absolutely *has* to make sure I'm the actual account owner, apparently...
Re: 2 syllables?
EDD for #1: 3/19/17
And personally- people aren't going to be calling her Marlow Etta Proudly all her life and mashing them together. So if you like it, go for it.
I agree but it's not unpleasant to hear or awkward to say. If you're ok with this (because it's accurate) then keep it.