Welcome to one of the universal frustrations of hosting. I will never understand why it's so difficult for some guests to RSVP, or why some people say yes but don't show, or say no but DO show. It's incredibly thoughtless, but it is an unfortunate fact of social life. And don't even get me started on thank-you notes.
With evites, there's always a chance that your invitation went to someone's spam folder or didn't make it to them for some other reason...although if you can see that your guests are viewing the invitation, so much for that possibility.
I always recommend one phone call or email to follow up, right after your RSVP date passes, because even the best of us can forget things. After that, assume they are not coming.
I have friends who, when people who failed to RSVP show up at the party anyway, sweetly say, "Oh! I'm so sorry — we didn't know you were coming, so I'm afraid we don't have a spare admission ticket/meal/favor bag/piece of cake/whatever." Personally, I have never had that much nerve, and I don't like to make a child pay the price for his/her parents' rudeness. I just make extra favor bags, order more cake than I need and hope for the best. It's up to you to decide which route you are more comfortable taking.
Oh, and the person who texted you? After this, delete her from your guest list. Permanently.