Name spelling

Miranda • Second pregnancy, due Jan 2020! I have a gorgeous 3yo girl too :)
I had an older customer come into work yesterday, and had to look up her details in our system. To confirm I had the right account I said 'Glenis?' (Phonetically) And she said 'No, it's Glenice - see it's spelt with an ice'. 
This lady was frustrated and whilst she could have just said yes and purchased her products and left, she felt the need to correct me, and say, exasperated 'so many people get it wrong and say glenis'. 
It made me think of all the mums on here who are making up unique/misspelled names for their kids and their many many years of frustration ahead. Please consider this before changing perfectly good spelling just to look different.