If your daughter isn't really young, don't plan on "being" with her. For at least 72 hours she needs to be in isolation. You can be in the house to help her like my husband did. You can cook for her and converse with her as long as you're not in the room with her. It's not safe to be with her. If she's really young, they'd keep her in the hospital to help her out instead of sending her home.
RAI isn't bad at all. I had no side effects. it was a pain to have to wash my clothes and linens every day, wear latex gloves with all electronics, shower three times a day and flush three times. But that was the worst of it. Make sure you use paper plates cups and silverware.
She'll be fine. If she does have side effects they are just flu like symptoms; nothing serious. I'm surprised they didn't do RAI to begin with. That is what will kill off all remaining thyroid cells; cancerous and non-cancerous. But at least they are doing it now.
Good luck and let us know if you have any other questions!