Ok I just started the Fighters Guild and for the quest to deal with the rats. For some odd reason when I try to speak to Arvena while she's sitting near the fountain it doesn't do anything. Can't talk to her at all. Do I wait for her to go to her house and then talk to her as I can talk to the person sitting next to her?

This is what the wiki says

Bugs

Speaking to Arvena Thelas before undertaking the quest while she is sitting on the bench outside her house may break the quest, causing her to never return to her house.
PC Note A possible fix may be to break into into Arvena's house. From inside the house, make the quest active. Open the console and use the command: getstage FGC01Rats. The returned stage should be 10.00. Then use the movetoqt command. You should appear outside Arvena's house, with Arvena standing right in front of you.
Alternatively, you can strike Arvena and allow yourself to be arrested. When you return to her home, she will have reappeared upstairs.
Arvena may also return to her house after the player waits or sleeps.