Iím not going to judge whether itís worth the hassle to get from Barcelona to Santo Domingo de Silos, butÖ
Can you tell me which page you were looking at? Iíll see if it contains any useful information. I gather that you have already found information on the BCN-RGS flights?
There is indeed a bus, but it leaves from the bus station in Burgos itself. She would have to take a taxi or a bus from Burgos airport to the bus station. (Options are listed here
The only regular Burgos Ė Santo Domingo line that I have found is operated by Arceredillo. (The line to Caleruega.) Their web page
shows that the bus leaves from Burgos on these times:
Mon to Thu: 5.30pm
No service on Sundays and public holidays.
For the return, the site only mentions departures from Santo Domingo at 8.10am. But it doesnít clarify in what direction (Burgos or Caleruega) that is? (But based on the timing I assume it's Burgos...)
If budget is not an issue, she could take a taxi from the airport to Santo Domingo de Silos. According to this website
it should cost a little over 100Ä one way.
Just to be clear, if never done any of these trips or used any of these services. I did spent some time in Burgos, but that was more than 10 years ago...