An update for those still following this thread....
Good news! It's Wednesday night and we are home after having the operation on Monday afternoon, so only 3 days in hospital. I can't believe how incredibly quickly our little 20 month old girl recovered! It was a hellish few days, trying to keep her happy trapped inside a cot with a million cables, IVs, drains coming out of her, slowing being removed day by day. She also reacted to the pain killers which made her very itchy (very common apparently) so that made her more unsettled and unable to sleep very much in the first day and a half. She was totally fed up with the whole situation by day 3, she is a very placid and quiet girl normally, but was having serious meltdowns and managed to finally rip out one of the IVs, luckily it was due to come out anyway as she had started eating and drinking well by then. So it wasn't fun by any means, but necessary, and completely worth it, as she is now cured! The operation itself went really well, they managed to do the operation entirely via keyhole surgery, it took about 2 hours, and they found that the mass/lesion was extralobar (outside the lung), so therefore a very straightforward removal leaving the lung completely in tact. This was the best case scenario, and as we didn't know what they would find until they went in, it was such a big relief to us.
This problem has been a dark cloud over our happy family for the past 22 months (we found out when I was 25 weeks pregnant), so to finally have this horrible source of stress removed from our lives is such a relief. We are home now, and she is a little out of sorts still, but doing really really well, and I imagine will be back to herself within a week or so, if not days.
I hope others who are waiting for their little one's operation have the same experience as us, with everything going so smoothly and a speedy recovery following. It will be difficult, but in the grand scheme of things, it is only a few days, and will fast become a distant memory with a very happy future ahead :)
Best of luck,