I'm sorry to hear about her mom, and my condolences to you and your daughter. The fact is, she's going to go through a lot, especially since she wasn't able to see her mother before she passed. I believe the LCSW should be sufficient, unless she starts acting out or things get worse then you may want to seek a second opinion from the one you have now. It's not uncommon for 8 year olds to be afraid of the dark, even without the loss of a parent.
One of the most important things to deal with is her guilt. Guilt that she may not even realize she has. Above all she needs to understand that her mother's passing is/was not her fault. You can mention this directly, and she might be surprised and say that she doesn't think that, but you can let her know anyway, there's nothing she could have done to prevent it, whether she was home or not. Children tend to take the worse things in life and blame themselves for it. I'm including some links below that might be helpful, and of course I welcome your thoughts.
Does she talk to you about it at all? Is she having any other problems?