First of all, this gal is "strong like bull" to be carrying all the heavy stuff! Wow, she's amazing! But there are many issues going on here...
Trip Planning: Starting someone off with a 14 mile day -- what???? Any time you haven't backpacked with someone before, unless you KNOW that they are a super-athlete, it's better not plan more than 10 miles for the first couple of days. I definitely agree with those who've proposed "baby steps".
Water: If she's really worried about contamination (rather than availability), why not have the two of you discuss (and research) different treatment options before you leave, and get her "buy in" to one or more systems. Let her see the science behind each method, so she'll understand. You might also start out by double-treating -- for example, use a Sawyer, then a Steripen on the same liter of water, until she feels more relaxed about it.
Extra Stuff: Encourage (not force) her to do a "post mortem" after each trip -- what did she actually use, what was never used, what would she want as a safety margin, what could be left behind next time. She should make a list. I still do this, and I've been backpacking for decades!
Heavy Equipment: Gear Swap! Post a WTB for a new bag for her -- I have a warm down women's bag that I would sell very cheaply to someone who would really use it!
Communication: Clearly, Rome wasn't built in a day, but I have to wonder if she feels like you're lecturing her (extrapolating from her not wanting you there while she's packing). Or maybe she feels that she can't keep up with you (14 mile day) and she's embarrassed about it. Include lots of praise for what she's done already, and talk about all the fun you hope to have with her in the future...
[Ed. for grammar]