My Casey is also 7 1/2 months old. She just recently (like the past 2 weeks) has been going to the backdoor when she wants to go out. I had a REALLY hard time potty training her though. I don't leave water out for them, I give them water 3X a day or so. After I give her water (I let her drink as much as she wants) I would put her in the crate for 45 minutes or so, then let her out to pee. That was the biggest thing that helped me. Also, and it might seem like a lot but I take her out at least once every hour. We are down to about 1 accident every other week. If I can think of any other tips, I'll post again. I know what you're going through...hang in there!!!
Also lots of praise and a BilJac liver treat....she'll do just about anything for one of those!