You need to at least give her a chance to raise the babies, but there are several things you MUST do to be prepared.
-Make sure mom is on a GOOD diet AND eating well. It also wouldn't hurt to start adding milk booster to her food now.
-Know the signs of rejection and watch like a hawk when the babies are OOP.
-Have a scale and keep a close record of their weight. If they are a low weight and do not seem to be gaining, but you don't see any signs of rejection, you can begin supplement feeding.
-Have your rejection kit ready so that you can take them in the event that mom does reject them.
Remember, it is always best to have the parents raise their joeys when possible. If you feel the last deaths were because of lack of milk production, this is not really rejection, she just may need some additional help.