You can see from all the responses that you got that she sounds pretty normal for 2.5. There is a pretty good series of books called Your <insert age here> Year Old by Bates and Ames. There is one for 2 years old. The authors say that around half years 1.5, 2.5, 3.5, etc, there is a period of disequilibrium in development so you get a lot of those behaviors you mentioned. I can tell you that 3.5 has been especially rough for us personally and I thought 2.5 was bad! It's not unusual for things like separation anxiety and other anxieties to occur at half years. Regressions on things are normal too. You know, it's hard to grow up and sometimes that scares them and they cling to babyish behaviors like wanting to be carried. Even though the Bates and Ames books feel a little dated in the tone, the behavior described is soooooooo familiar! For instance, my daughter went through a face where she would yell things at me like, "I don't love you anymore!" And the 3 Year Old book addressed it specifically. LOL I was able to quit taking it personally after reading that.
Anyway, how to cope? It's hard to be calm, but that's the best thing to do. I know that if I wake up in a bad mood or I'm having a bad day, my attitude affects how she acts. When I make an attempt to be positive, it's sets the tone for a more amicable day. Focus on the positive things she does as much as possible. Along with that, I would resist the urge to complain about her in front of your husband; do it after she goes to bed. I was guilty of that a lot until I made the effort to stop. Instead of listing all the challenging behaviors she gave me when my husband got home from work, I would try to say something positive like, "Daddy, guess who helped me fold the wash cloths today? She did a great job helping me with the laundry." I don't like focusing on bad behavior because I feel like it sets up an expectation for that bad behavior to occur.
Listing your expectations when you go somewhere is also an excellent tool. I used to do this for things like the grocery store or a restaurant. Remind her of the way we behave at a place. For a restaurant, some of our expectations were that we stayed in our seat and didn't run around and that we didn't yell in the restaurant. Have her repeat the rules back to you. Try not to be embarrassed by her behavior. Really, your friends with 2.5 year olds will understand! The weather is getting nice now. When she's getting under your skin, take her to the park. A change of scenery often works wonders.
I would back off the time out as well. We hardly ever use it. In our house, it's reserved for serious offenses like hitting. (You hit, you sit.) Otherwise, we use more direct consequences. Play with a toy inappropriately (like throwing hard toys around the baby), then that toy goes in toy time out for a while. Splashing water out of the bath when you've been reminded not to, then bath time is over. Stuff like that.
As for potty training, back off for a while. Maybe she is also resisting because she is having anxiety about growing up if you are repeatedly telling her that babies use diapers and she needs to use the potty like a big girl. She may be clinging more to being a baby because being a big girl is scary. You're home with her, so is it very important that she be potty trained immediately? She'll get there when she's ready. My daughter was day potty trained very close to 3 and more consistent about it a bit after 3.
She will get easier again as you approach 3 in my experience. And then she'll pull a Jekyll and Hyde on you again as 3.5 rolls around! Hang in there!