Issues with a female friend Note: Long winded tale

Howdy guys and girls,

I apologize in advance for spelling mistakes and for any bad grammar I tried:D.Well to cut to the chase a female friend I have,was seeing a guy(we'll call him Bob) last year anyway things didn't work out with him mainly cause he treated her like dirt.So she broke up with him and started seeing another guy for a few months things didn't work out with him.So as she was very down and out she went back to Bob a few days later but this time it was as "friends with benefits".

So that went on for a while till she found a new guy her current bf and ended it with Bob.But another girl got in touch with her via Facebook months later and told her she was seeing Bob around the same time as my friend.So my friend found out he cheated on her (I dunno if it's classed as cheating if it's friends with benefits) but Bob is still texting her months later to meet up and she texting back seeing if he admit to cheating to her.
To make matters worse she found out that Bob had a gf at the time(who she's still seeing) while he was seeing the two girls who happens to be heavily pregnant so my friend announced today she had gossip she found Bobs girlfriend on facebook and "Shes 31 and not that pretty" (very catty comment I know shes 25 btw if it matters).

Anyway my mate wants to tell Bobs girlfriend that he's cheated on her and I said to her you might get abused or worse if you just said to a girl that accusation.She agreed she said she's gonna get someone else to do it tbh I think she is going to do this all via facebook and not in person.Hope all this makes sense .


We kinda disagreed on this next part I said to her it's not fair to tell a girl who is heavenly pregnant about him cheating months before I know the guy is a tosser etc etc and if it was any other circumstance I'd agree with her to spill all but I'm just thinking about the pregnant girlfriend in all this.She said if she was pregnant she'd want to know and I was saying no two people are the same.

I know there is never a right time to tell anyone this but to tell a girl when she's heavily pregnant I don't think my friend should do this to her.Tbh I see it more out of revenge to Bob then to warn the gf about him.Plus I told her she has a new bf now new start she should just move on with her life and forget about him but I think she just hurt about all this cheating.She said she wasn't going to do anything drastic yet!

Is she right to tell all months later or am I wrong with my opinion on the whole matter(I'll apologize to her if I am because she was quite upset about it) or this might be the case there is no right or no wrong answer .Thanks in advance your advice is greatly appreciated.