So you're not even sure she would want to live with you yet and just assuming your H will try to make it happen,right?

This gives you time to figure out how you will handle it if it does.You can use this time to prepare a list of rules,what boundaries you need to set,whether you will have her contribute income towards bills,whether she will contribute towards household chores,decide how long she can stay,etc.Doing that ahead of time(just in case) will make you feel more in control of the situation.

If you just absolutely don't want her there at all you really need to speak up before it happens or it will turn into a disaster for everyone involved.

Are you close to her?Do you two get along?