She has a non-native accent but it's indistinct. Shohreh Aghdashloo who plays Shala'Raan is Iranian and they speak similarly. Han'Gerrel, Zaal'Koris and Daro'Zen all have English accents while Kal'Reegar, Kenn (Kenn's salvage), Veetor and the quarian women you see on the Citadel and Illium all have American accents. It's confusing.
This is probably what bothers me... like that Fleet and Flotilla movie she's obsessed with.
Slightly pedantic correction: Daro'Xen's actor is Australian
I chalk it up to quarians not being a monoculture. They are clan based, and it isn't unreasonable to assume that there are differing dialects of Khelish just as there are for virtually any other language. Most of the inhabitants of the Rayya (Tali's birthship) tend to have a similar inflection to her, for example, as does Rael'Zorah.
*shrug* I like some chick flicks and don't think it makes me into a weak, cutesy or immature person.
I believe the reason why they have different accents is due to the fact that the Quarians who originally escaped Rannoch could have come from all over the planet.
As for Fleet and Flotilla, I like how she loves it. She's in her twenties, and unlike in ME1, where she was nervous all the time around you due to the fact that she had never really met a human before, either has a crush on the male Shepard or is in awe of FemShep, and is away from the Flotilla for the first time on her pilgrimage. In ME2, she matured a lot, and wasn't too impressed or intimidated by the people she had met after the events of ME1. When Shepard comes back, it's special for her due to the fact that they were her captain during her pilgrimage, and that she never really spent to much time with you other than the short time on the SR1. She acts normal around FemShep and trust her as a close friend, which is why she occasionally shows her childish side. As for male Shep, she has a crush on them, and considering that Tali, as far as we are aware of, has never had a crush or dated anybody, she gets nervous in ME2. By ME3, she retains the friendship with Femshep, is comfortable in a relationship with a Male Shepard and shows her childish side occasionally, and can be a good friend with a male Shepard who doesn't romance her due to the whole "captain" thing.
Now despite the fact that she she shows this childish side if you gain her friendship, she also shows her more mature side. She can act very serious sometimes, and has a pretty good range of emotion. She can get pretty angry as well as sad, and if you romance her she can occasionally act a little sultry if I remember correctly.