8C's do not have obstructed views, and she should have let you pick your exact cabin if you wanted to. Carnival does
allow you to book the available cabin of your choice.
She might get some perk or something booking her customers in guarantees, but she should let you know that you are allowed to get an actual room number if you choose!
I'd can her and find a different travel agent.
I've found one I love from the Bargain Finder here at cruisemates.com. I haven't been with her long, but others who cruise a lot can recommend good ones. Just Email people who rave about their agents, there's lots of threads.
Or you can talk to mine if you want. We're not allowed to post names.
Travelocity.com has a great little light-up deck plan feature that highlights which cabins are available. See if they have your cruise available to find out what 8C's are still open and get an idea of where you might be.
Guarantees are a good thing if you're not picky and don't mind waiting until the last day. My next two cruises are guarantees by choice, since there is the small chance of getting an upgrade. But, your travel agent needs to be more honest and informative with you.