You sound like a really good friend and it's great you provided so much support when your friend needed it.
Just to provide another perspective though - even though she may be "doing well" as a single mum, it doesn't sound like her struggles are over at all. Even when you have your life together, being a single parent is still exhausting, scary, a huge responsibility and a huge effort every. Single. Day. With four kids, a job, probably no support from the father given the history of DV... wow she deserves a medal just for making it through each and every day.
I'm "doing well" as a single mum - work full time, comfortable financially, have time to myself when DD goes to her Dad's every second weekend... and there are many many days where I feel like everything is going to fall apart and if one tiny thing goes wrong the whole house of cards is going to come crashing down. And I only have one child! I have no idea how your friend does it with four and a past experience with DV.
So while it sucks that she can't be there to support you, and you no doubt deserve that support, try not to take it personally.