Hi.
My name is S.. I am a teacher. I've taught 4th and 5th grades. My divorce was final last December and I have two girls, Cate (5) and Sophie (3).
First of all, it's obvious that you're a good mom. This is a very stressful time for you and your family. It may not get better right away but things will change. Nothing lasts forever, even hardships.
So, I thought that Cate was having a hard time with the divorce so I spoke with a therapist. Her first question was how is she doing in school? Since Cate's doing fine and there's no problem there then the therapist thought she's doing okay. I tell you this because your daughter my be having trouble as a result of the stress of your family situation.
I suggest you first contact the guidance councelor of the school. Ask her (him) for help with resources (a school group, Rainbows, etc.) for your daughter to help her deal with her changing family.
Next, speak with the teacher and ask if there is a way to test for any learning disabilities to rule that out. Also team up with her teacher and have a weekly or bi-weekly "progress" report. I have given "special" homework for parents. Parents are not teachers and we are very busy and tired. This is just a little something you can do every day to help with your daughter's reading. This is a specific short activity (10 minutes tops) that you can easily do with your daughter.
Finallly, incorporate reading in everything you do with your daughter. We read all the time without even realizing it. We read street signs ("What letter does the STOP sign begin with?"), directions for cooking dinner ("Can you circle all the capital letters in the directions on this box?"), and reading stories ("How many times do you see the letter 'E' on this page?").
I hope this helps. I know it can be overwhelming to do everything on your own. Ask for help from your school. That's what they're there for.
Good luck!