That's a tough call... normally.. I would say wait a bit.. be there for her as a friend...
But.. each situation is different.
Here's my story:
Jackie, Robyn and I were all friends.. and would hang out on occasion. (we all worked together at some point as well)
Well.. Robyn and Jackie split up.. (just drifted apart) and.. well.. I saw no reason to take sides.. so I kept talking to them as usual. But.. my heart went out to Jackie more just cause we always just kinda clicked and Robyn just kinda left her for no reason. We started hanging out on a regular basis.. and the first day we hung out there was a sense of something there. (sexual tension, anyone? :chuckles: ) But it was more then that.. there was a bond there that perhaps was just growing stronger now that we were both single.
And.. well.. after a month or so we acted on it. I was fighting tooth and nail because I liked being single.. and didn't want to go behind Robyn's back... (but we later found out she was dating some bi chick anyway.. so.. ****it. ) But.. I knew she was too good to pass up.. so I eventually succumbed to her charms.

Keep your mind about you.. and keep things normal... don't shy from hanging out with her... and keep your eyes open for little hints of things.