I wouldn't, especially if they are already hatched. I would worry too much about the chicks health. Sometimes you can add day-old chicks to a broody hen in the night, but I don't think that applies to this situation.
If you decide to try, there are threads talking about adding day-old chicks to broodies on this page. I would follow those guidlines and watch her carefully.
If your hen is a good mom she will accept any babies right now especially if they just hatched. I have a hen that will take orphan babies that are 2 or 3 days old at times and mix with her babies that she has hatched. Usually if they are older than that they will peck the babies to make them go away from their brood. Somehow they "recognize " who is what. I always try and place them at night under her in the nest box so when she wakes up all of her kids are there !! She is a 1/2 Japanese Bantam and Buff Cochin cross.
Just wanted to let everyone know that she took to the other chick just fine. I moved her to a bigger cage with new bedding . She satarted digging around when I got the other chicks in there with her. Put the new chick in with her she looked at the new one and just went on with what she was doing. It has been about 6 hours now and they are doing just fine. She is one good mommy. Thanks again for all of your input.