How about another app on the phone that is like a simple "Instagram" or "snapchat" where apart from her sending you pictures, you can see pictures she has posted of what she is doing daily to further drive home the moments where she is not telling you the whole truth (im even imagining at some point the MC makes a fake anonymous profile to see if his GF has hidden posts or stories from him and she has). Maybe even a app like "google maps" to track her location? sometimes couples permanently share their location on apps like that. This sounds like a boatload of work so I know this stuff isn't easy, I'm just spit-balling here.