I'm struggling with how to handle this situation and it's incredibly awkward because I work with her.
Started to meet regularly with colleague outside of work as her DD is the same age as mine. I struggled to get on with colleague at first as she's quite a confrontational, angry/frustrated person in nature. She said we should meet and I thought I might as well, I may be jumping the gun a little and would be nice to get to know her.
Long story short she's still an angry person and absolutely draining to socialise with. Says incredibly inappropriate things in front of the dc and is a total dick towards her dc. I know it sounds harsh but the things she's said and done in front of us is unsettling, embarrassing and I just don't want to socialise with her. Nor do I want my dc near hers because her child is also pretty aggressive and my dc doesn't like her.
The way she treats her dc isn't something social services would be able to do anything with because it's more shitty, lazy, old school parenting and belittling her dc.
But I work with her and she's already asked me several times when we are going to meet again. I'm a total coward and have just responded with "we'll have to arrange something soon". 
But I can't say that forever and she thinks our dcs are best friends and keeps guilting me saying X is desperate to see Y.
No idea how to move forward...