This screams of her wanting you to stay right where you are in her head.
Any normal decent friend would be shouting from the rooftops about how far you have come, how your DC are a credit to you and to their father.
If you stay as you are, it means that she stays as she is. if you move on, then you are leaveing your place, and potentially competitive somehow.
it could be as simple as her own insecurity:
Widowed is a status that deems you 'off the radar' somehow. when you are 'dating' that means that you are now SINGLE.
Divorced women get this all the time, the fact that you are not partnered means that you are a loose cannon. She has now gone from seeing you as benign to seeing you as a threat.
Some of us live have experience of family and friends being happy for us as long as we remain 'down' or oppressed/suffering. the minute we begin to rise/get on with life/recover, this causes them extreme discomfort and we can't be allowed to do so somehow.
I know it's trite, but it rings true sometimes that some people are in our lives for a reason, others for a season and the best for life.
If I were you, I would sit her down and tell her how hurtful and negative I'd found her comments and that it's causing you to question everything to do with your friendship.
then I would take a VERY large step back. knowing someone ISN'T cheering for you, personally or for your your family is a nasty acidic presence in your life, and will eat away at any self confidence you gain.