How should one react in this situation (see details)?

A bit of background:

I found out from a friend that one of my best friends has recently become pregnant, for a second time. I adore her son, who just turned three in February, but I can’t be happy for her over this pregnancy.

She recently had relationship problems with the father, whom she is not married to, and cheated on him. They proceeded to break up and get back together I don’t even know how many times over the past 4 months. In addition, I have never liked the guy she’s with. I don’t think he treats her well enough and there is a question of abuse in the past.

They are not in a good space financially and I feel like they’re trying to use a child as a “fix” for their relationship.

How should I react and what should I say when she tells me herself? I don’t want to say anything that would upset her or jeopardize our friendship.