There are a number of reasons why she could be going on match.com
First of all, you are going on it too. You stated you have a profile, she may be checking to see if you're going on it in the same way as you're checking to see if she goes on it.
Why have you not deleted your profile?
I think the important issue is whether she's subscribed to it. If she still has a profile and not subscribed then maybe she goes on it when she gets a notification via email, this then registers her checking into the site and you're busy nosying around to notice how often she's clicking on it.
I had a similar experience in that I met my last girlfriend through internet dating, but still had some old profiles from a couple of years beforehand on other sites. I should have removed them, but didn't as some of these sites were difficult to remove yourself from, I also had others that took my profile and transfered it to another site without my initial knowledge. Really i should have spent an evening going through them and removing them, but as i had no interest in meeting anyone else I just left them.
Occasionally however I'd get a junk email notification, i'd click on it which would then register my clicking on the site with the date, etc. Sometimes i'd try to navigate to delete myself. Unknown to me my girlfriend through her own insecurities spent an evening searching for me on different sites adn you guessed it, she came across these old profiles, saw that i'd clicked on them after we'd met put 2 and 2 together and came up with 5. She never told me about what she'd found, but allowed it to build up over a few weeks, began not to trust me and started checking things. She'd found an empty box of condoms, that we'd used a couple of months previous, accused me of cheating and finished with me.
I can honestly say that I never so much as looked at another woman whilst with her, but she let her imagination get carried away without talking to me. Things have come to light since that she had in fact herself cheated on me, but that's another story. The instigator and start of all this was her looking for me on internet dating sites.
You really need to talk to her, not us on a forum platform...but HER. She maybe cheating, who knows? But right now all you've got is titbits of info and your imagination. If you want to make a go of things with her, you both need to come off match.com