Normally, it is possible to travel to the U.S. on ESTA on a business trip during the time before a person is granted a work visa, but entry is not guaranteed under ESTA in any case. At the time of entry she will be asked what her purpose of traveling to the U.S. is, and if the CBP officer does not believe her (or believes she is actually going there to try to start work “early” before she gets her work visa), then she would not be admitted. So it’s important to understand all of the facts and for her to be prepared about what to say if she is questioned at the airport when she arrives.
Sometimes we provide clients with letters to present to CBP if they are questioned. If she is denied entry under ESTA because the CBP officer does not believe that the purpose of her travel is appropriate for ESTA, then she should still be able to apply for a work visa, however, there will be a note in the CBP system under her name so she may experience delays and/or questioning in connection with future entries, and of course, in the process of applying for subsequent visas, she will need to review carefully the wording of the questions on the online visa application (Form DS-160, and be sure to disclose that she was refused entry if that is a question on the DS-160 at the time she completes it (the wording of the questions on the DS-160 changes from time to time).
Besides this, if she is planning on traveling directly from Europe, she would need to obtain a National Interest Exception (NIE) because of the travel ban. Since she would be traveling on ESTA and not with a B-1/B-2 visa, the NIE would be applied for with CBP, and the method would depend on the U.S. airport she will be flying into. For the NIE, it would need to be shown that her travel to the U.S. is in the national interest as understood by the CBP, for example, it would provide a significant economic benefit to the U.S., support the fight against COVID, etc. This may be trickier to prove for someone traveling on ESTA (as opposed to a work visa) because that person will not be “working” in the U.S., so we would need to explain what the specific reason for her travel is and how it is in the national interest. The CBP may view this strictly. If she instead seeks a B-1/B-2 visa to travel for business, she can apply for the visa at the Embassy in Vienna, and at the same time as she is applying for the visa, she can request the NIE from the Embassy, in which case is it not necessary to request the NIE from the CBP. In a case like this, it may possibly be somewhat easier to secure the NIE from the Embassy, as the Embassy will likely be more familiar with the Miba organization and it specifically notes on its website that NIEs are available for “B1 visas (for travel that provides significant economic benefit to the United States only).”
Alternatively, she could try spending two weeks in a country not subject to the travel ban before seeking to enter the U.S. with ESTA, then it would not be necessary to obtain an NIE from the Embassy or the CBP.