Ok, womens bikes are a bit of a swamp of info. Some people think they're just a marketing tool, others that they meet particular needs.
Different brands go for differing levels of customisation on their women's specific bikes compared to the mens equivalent, but from what I can tell female specific road bikes are usually closer to their male equivalents than with mountain bikes. Women's road bikes usually have a slightly shorter TT length (only by 5mm or so it would seem), and a slightly wider/shorter saddle fitted, whereas on mountain bikes it often goes a lot further with more extreme frame geometry, narrower bars, thinner grips, softer suspension, different tyres etc.
Personally, I'd buy a bike that fits, and not worry whether or not it's female specific. That said, if you do find a girlie road bike that fits well, you'll save yourself a few quid on having to replace the saddle at least.
Onto the rest of the specs... First question, how much road riding have you done before? Second question, how much are you likely to do? Thirdly, how fast do you want to actually go?
I'd view 10spd as a "nice to have" rather than a necessity. To be honest, I'm still amazed just how well my 9spd Tiagra works. Its miles better than the Deore level MTB equivalent in smoothness and function. And the difference between only having 9 gears and 10 gears is less noticable on a road bike than on a mountain bike oddly enough. If a 9spd bike came with too small a cassette, you can always still buy a lower ratio cassette to help get up the climbs anyway for £25 or so.
I'd also consider a triple rather than a double chainset. Compacts are a halfway house, that IMO (and I've got one) are neither one thing nor the other. I often find I'm riding along thinking the 34T chainring is too small, and the 50T too big, so I'd like to be sat riding along in a gear inbetween. The triple, with its 30/39/50 ratios, offers just that, and still has the outer ring for top speed, but also a slightly lower ring for helping get up the climbs too, and all for less than 1/2lb weight penalty. If of course you've got thighs like Chris Hoy's, and think nothing of averaging 25mph on the flat, then ignore everything I've said, and get a 39/53 double setup instead.
With a bad back to consider, and I'm assuming the money you're planning on spending on the bike and the questions you're asking you're not planning on winning any events, I'd not look at something full on head down arse up. Something with slightly more relaxed geometry, or "sportive geometry" as it's often known, will suit better. Top Tubes are usually a tiny bit shorter, head tubes longer for a slightly more upright stance, and they often come with shallow drop bars.
I ride a Giant Defy 2 myself, which fits most of the above criteria and is a great bike for the money. They also do a women's version called the Avail. Would happily recommend either to anyone looking for a first road bike. There's also a few bargains around too right now. Giant sizes work slightly differently to normal as they're "compact", so if you need a 50cm frame normally, you'd need Giant's 46.5cm (S) frame, or if you'd normally ride a 54cm as I would, you need their 50cm (M) frame.
Something like this would suit the bill perfectly I reckon, or the female specific version of the same bike... Whichever fitted better, and you preferred the look/feel of.
