Yeah don't do this. Be a grown ass adult and just end the relationship.

You won't "end her career." She'll get an article 15...maybe a field grade. She'll lose rank. Oh well. She'll have it back inside of a year since she's probably, at the highest, a PFC maybe a SPC. She'll easily bounce back from that, pcs to her next duty station and it literally won't matter. You're her boyfriend not her spouse. She's not committing adultery and unless she's really fucking dumb, she's not fucking cadre.

She'll probably get caught on her own by being a fucking idiot.

Also, as it turns out, screenshots of location aren't the rock solid evidence you think they are. They can easily be doctored. Also, tracking someone on an army base is...kind of a grey area.