my 2 cents based on our experience:
Find out what exactly scares her (e.g. pain, side effects, weight/backpain). In our case she didn't trust her already used doc/clinic to be good with bigger ones plus some side effects…
Great doc that can take the concern away is key. But you have to take the first hurdle to get her to a good doc for a consultation.
Best I learned is for her to chat with girls that are big and happy with it. In our case we went to a gogo bar together, to look for suitable boobs for her. After some drinks and tips 2 girls were happy to share their experience with her. This didn't take the fear away but she was then sure she wants more. In our case she then got her first set, maximum size she could take for the first time. 6 weeks later she added 2pcs 150cc silicon pads in the bra when she was in dress mode. That got her to the level the stripper she talked to had.
That in combination with some research (together) for a more suitable surgeon let to the decision to go bigger this year. Aim around 1000cc now (at 47 kg).
Obviously, if she goes for her 1st job, be there, pamper her, make it easy for her. So she will be ok for the upgrade some time later.