If I'm totally off base on this, then forget you ever read this.
My thoughts are that this lady is a Christian who is trying to express something heartfelt to God and as such, has written what she sees as something pure, simple and uncluttered that isn't really designed to draw attention to her or itself. Whatever the wrongs or rights of that view, it's a view that has been prevalent in 'christian' music since the dawn of the rock era and partly accounts for why so much music of that ilk is so sterile, unadventurous and unappealing. Fortunately not every Christian has been that way about music but a sufficient number have for that kind of thinking to be underscoring much music by people who happen to believe in Christ.
So from that perspective, I can fully understand why she just wants her voice and guitar. By doing what you've done, you've taken away the intention and focus of where she's coming from and chances are, she may feel that those she might want to share the song with won't catch what she wants them to catch.
From a song point of view, I find it a monotonous song. It sounds like a thousand and twelve songs I've heard a million and eight times and zoned out, predictable chord structure, changes, climax etc. The violin and pad {maybe not so much the strummed guitar} certainly save it from being a total snore and actually really enhances it. It gives a listener who may be totally opposed to the core of the message something else to focus on and possibly enjoy without feeling that they're being imposed on.
So yeah, from where most of us stand she's making a bad decision because a dullish song {in my opinion} will be rendered even duller without some adornment. But, from her perspective, her request makes abundant sense, mores the pity, but it does.
Give her the copy she wants and keep the one you feel is the better. It's not unusual in music recording for the artist and the 'producer' to not see eye to eye about what they've worked on.
Funny thing though, one day both of you just may be glad that you did keep it.