A general rule of thumb is that any communication initiated by you right now is seen as pursuing.
Think about this: Does W know that YOU know she's staying with OM, broken? If so, think about things from her perspective: H knows I'm sleeping with OM, and he's STILL showering me with compliments! I have TWO men interested in me, and both are begging for my attention. This is toooooo easy! I love the attention! I think I'll just keep doing things the same way for a while ...
Now, if you see her in person and notice she looks nice - especially if you, yourself, are feeling confident about how YOU'RE looking - I, personally, don't see anything wrong with a passing, "Dang, W. Still lookin' good in yellow!" And just keep walking, without expecting a response.
The fact that she can see you walking away after saying it, upbeat and carrying on about your business, makes a compliment like that preferable to be said in person than in text.
You definitely don't want to come across as desperate or trying to "lay it on thick" while she's in an active A.
