It sounds like she is bored.
She had a regular routine going at school and now that she isn't there it's hard for her.
Try making a schedule for her for the daytime. I had to do this for my kids for a couple of summers. It worked nicely. We had a craft time, nap time, clean up time, reading time, quiet time (they could nap or do something quietly during this time). Also schedule lunch and dinner. And a free time should be included too.
You don't have to be strict about the schedule, but if you make a simple one, and try to stick to it, you will probably see a difference in her.
Also check with your library, most offer reading groups for kids her age. I'm sure her brother would enjoy that too.
If they don't offer one, do it yourself. Go check out books that are age appropriate and set a reading time with the kids.
Take them on 'field trips' to the park and such. Since you are a SAHM, it's a little easier for you to follow a schedule with them. Just include different activities for them to do each day.
Example schedule I had was:
8:00-9:00 a.m. Breakfast
9:00-9:45 a.m. Craft time
9:45-10:00 a.m. Clean up
10:00 a.m.-11:00 p.m. Outside Play
11:00- 12:00 p.m. Reading Time
12:00-1:00 p.m. Lunch
1:00-2:00 p.m. Free Time
2:00-3:30 p.m. Nap/Quiet time
3:30-5:00 p.m. Outside Play
5:00 Dinner
Evenings should be family time with you and dad.
I hope this helps you out.
Good luck