I think you've done about all you can do to break her broodiness...one trick I've used with success is to gently remove them from the nest and place them into the middle of the yard/pen and immediately feed them their absolute, to die for, treat. Keep doing that regularly about 3 times a day. They should view this as a gift from heaven treat experience, not punishment (positive reinforcement technique I learned with dog training and have applied to chickens with some success). Timing is essential...placed in yard equals heavenly reward. Place them in the same place each time. In a few days invariably I see them running to me for the treat as I step into that spot. Within a week, I see them lingering in that spot. It is positive reinforcement for getting off the nest, but it has to be a "to die for treat" not just regular food as they won't be interested and the timing as to be immediate...out in yard...immediate treat. (Dogs have a 3 second retention learning enforcement period...I suspicion birds have shorter.)
The other option is to place the chicks with her. Smaller than a grapefruit to me is big...as we see large grapefruits in the store...so I am going to assume you've got typical 4 week old Silkie chicks, which means still fairly small, and likely partially feathered. I would try it but stay close by and watch. Since you don't say where you are located, I can't recommend evening or day as I find the weather contributes to my fostering success. Warm weather I place at night. Cool weather I place during the day. Small babies under the brood lamp often are fearful of the big scary hen at first, and since they don't regulate their body temp well, they can undergo quite a bit of physical stress as they figure out she's okay to go to...I have had chicks succumb to the environment stresses after several days of being with an inviting hen in cool weather. (I pull them out dead from under her). I do better in warmer weather.
Good news is your chicks will have some feathering. You also can add a heat lamp in your coop if it is safe to do so and that allows the chicks to run to mom or stay by the lamp. (Be careful though, I've burned down a coop that way, and so have several of my friends...always when a chicken knocked it down into the straw.)
Watch and see if the broody clucks and invites them...since she is soooooo broody, chances are she will...but as your chicks are older and very skittish, chances are it will take them a few days to learn to graft to her, if they ever do....but she may be so warm and there may be enough natural imprinting instinct left for them to do so...however watch carefully and frequently...if you see them huddled in cold away from the hen, you know it isn't going well.
EDITED TO ADD: I would also provide vitamins/electrolytes in the water to help booster their immune systems for the shock of the change. With small chicks, I literally dropper load them then place them so that they are well hydrated before the stress of change. You might put the nummy Chick Saver in the water and let them tank up just before you place them.
Good luck.
Lady of McCamley
