You've got other good answers about whether you're able to "fire" her.
What I'm confused about is her strategy. On the one hand, you say she suggested the higher price and "she stands by her price." OK. No showings in 3 weeks, and she's probably wrong. It's probably priced too high. Still, you say "she stands by her price."
You've seen comps showing lower prices, and two previewing agents said it was priced too high. Agreed, it probably is. So, again, why is she "standing by her price"?
On the other hand, it doesn't sound as if she's standing by her price. You say she'd said that if you had no showings then "I need to reduce the price." She's sending you comps showing a lower price. You say she's asking "for a reduction."
I think there's some miscommunication here. Either she's telling you: "$274,500 is a good price and I think you ought to keep it there" or she's telling you "$274,500 is priced too high, and I think you ought to reduce it." She can't be telling you both things.
So, talk to her. Ask her: "Based on the input you've received thus far and the lack of showings, where should my home be priced so I can reasonably expect to receive offers and have a good chance of selling the property within 60 days?" Use that exact, precise language. If she suggests a number, fine. If not, say: "I'm looking for a specific number. Please give me a specific number."
Then, when she does (if she does), you respond: "If I am understanding you correctly, you are saying that if my home is priced at $____________ that I have a good chance of selling my home within 60 days?" If the answer is "yes," then at least you have a real number. And, from your question, it's apparent you have a good idea of what that number ought to be.
Then you can make a decision about whether you want to continue with that agent or whether you'd feel more comfortable with another agent.
One other note: In your situation, at $25,000 price reduction won't make you look desperate to sell. Many agents who look at the price reduction will react along the lines of: "Those sellers apparently were a bit greedy to begin with. But now they've seen the light, and priced their home competitive. Now when I have a client looking for a reasonably priced home, I can include this one on the list." (I know it wasn't you being greedy to begin with; I'm just telling you how many agents will react. Still, they'll be pleased that your home is now competitively priced. It'll give them another one that they can present to their buyers.)
Hope that helps.