I've actually bred Strawberries before. Are these wild-caught birds, or are they F1 or F2 captive-bred birds? Do you have current photos of your set-up and the birds. Strawberries like most waxbills prefer to line their nests with white feathers. It's possible she used her own to line the nest. Handfeeding finches is notoriously difficult. It's very easy to aspirate them and often time they appear to die for no reason. I would recommend doing a lot of reading. The Finch Forum:
http://www.finchforum.com/ is an excellent resource and there are several breeders on there. There is also a Facebook group for Strawberries and Gold-breasted Waxbills although the name has escaped me at the moment.