A couple of questions you need to ask the principle and teacher of the class.
1. Is this a self contained classroom. That means four walls and no other class to share the space.
2. Has she done this before and with first and second graders and how did this experience go for her? A biggee question! How experienced is she?
3. What type of teacher and teaching does she use. Is she a sit down at the desk only teacher or does she let the sit on the floor, have general work time, work in groups, work at their own speed in some areas, work in collaborative groups sometimes?
4. Does she let/need parents come into help regularly for small groups while she works with other kids?
5.And finally how big is the class? Some times the class is smaller because of the mixed grades. That is a good thing.
My concerns also include. First graders at the beginning of the year are skill-less. Meaning they need to learn letter sounds and how to make them, basic math skills and concepts. These skills take up almost all the day (former k-1 teacher here) so how is she going to balance her time? This is a question you need to ask her.
I am not against multi-grade classes. I always taught in them. I hope that I have given you some good questions to ask. I think multi-grade classes are good if the teacher and conditions are right.