You're 25 and you're suspecting that your girlfriend is doing something on Facebook that you might not like, the approach you want to do is most importantly an awful thing and will separate both of you even further and secondly, its immature thing to do, if you are insecure about it, then TALK TO HER about it...
MPGH isn't a consulting website where you get help for your troubling issue/issues with relationships, family and/or other things, if you can't talk to her about it, then she doesn't deserve you, talking to your partner and not being afraid is the best way to secure the relationship, and most of the users around here are no older than 18, so your help resources go down by a mile