How about something she can pamper herself with? A selection of creams and lotions maybe. You can get sets with pregnant mums in mind. Another idea would be to maybe give her a gift certificate for a salon to either have her hair or her nails done. The gift certificate could be for a shop where she could either spend the money on herself or baby, i.e. Blooming Marvellous, that way you wouldnt be directly buying for the babies but she could use the money to get something that will be needed once they arrive herself.