Talk with your daughter one on one during some quality bonding time. If your schedule is very busy, even if it is not, mark your one on one time is on your family calendar to make sure you really have it.
Don't just stop with this though. Your school has professionals who care about your daughter, her teachers and the school counselor. You said this change was during this 9 weeks of school (1st quarter). Check with her current teacher to see who she is hanging out with at school and ask for any observations. Teachers are great allies in helping parents with children. You might even check with her teacher from last year who might be observing your daughters changes.
Every school has a counselor, make an appointment for you alone to see the counselor to discuss concerns and observations. Then, possibly, a follow-up appointment that includes both you and your daughter. Or even just your daughter alone (she is of an age that she might talk to the counselor alone about what may be the root problem.)
Don't forget the family doctor. They can be a great resource too. A phone consult with a possible follow up appointment might be needed. She may have developed a medical problem that you are not aware of. Two of my nieces developed some medical problems at around that age.
Good luck!!