Thanks everyone! All the answers were very helpful, but I think I need to rephrase the question...
We want to know if she can visit while I29F is being processed (not the K-1, we know she can visit while that part processes). So the petition part, which is the I29F, which we understand can take up to 4-5 months, can she visit while that is being processed, pending approval? To put it another way, can she visit between submitting the I-129F and receiving the NOA2.
Many thanks L+T, LizandNate, JS&PL, Randy and Kim!