Definitely pregnant. I would say she should drop within the next few days. Keep a close eye on her. When she is about to drop she will start trying to find places to be alone and won't be so active. She'll also probably stop eating.
Not sure what your plans are, but is it possible for you to get her in a tank by herself? This will be a lot less stressful for her when she gives birth than a breeder box would be. Plus, once she is done giving birth all you have to do is take her out and then the fry will have a nice spot to grow without you having to worry about them being eaten. That's what I have done anyway. Momma guppy was happy as a clam and the fry are growing like weeds.
Keep in mind it could take her a day or two to finish dropping her fry. Stress can slow down the process too.
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