In reply to jenniwat001: In reply to jenniwat001: Hi Jenni, there is unfortunately not that many women's specific belay jackets out there but as a starting point here are a few thoughts.
Most people will go for a synthetic fill garment, as down although having the best warmth to weight ratio, looses much of it's heat retaining properties when wet. Waterproof down garments do exist but the waterproof shell adds considerable weight, bulk and cost. More details on insulation here:
http://www.ukclimbing.com/articles/page.php?id=5105
So synthetic fill is probably best, but how much do you need? Well this will depend on how hot you run and what other layers you are using. However as a generalisation most brands go for 100g in the body, with perhaps 60g in the arms.
As I said above if you want a women's specific jacket then you have a shorter list to choose from. However, as a belay jacket is designed to go all your other layers, a womens's specific cut may not have much relevance as the jacket simply needs to be 'big'. Also on cut, just like men's jackets, various brands will have differing interpretations of a female cut, and therefore trying the jacket on is vital to find one that fits you, especially when your wearing your other gear.
Female specific, synthetic belay jackets to consider (some already mentioned above) listed roughly in order of warmth:
Mountain Equipment Women's Citadel Jacket:
http://www.mountain-equipment.co.uk/the_gear/clothing/insulation/womens_cit...
Arc'teryx Women's Atom SV Hoody:
http://www.arcteryx.com/Product.aspx?EN/Womens/Atom-SV-Hoody-W
The Mountain Equipment Women's Alpa Mayo Jacket is also good but not as warm as the Citdael.
http://www.mountain-equipment.co.uk/the_gear/clothing/insulation/womens_alp...
The North Face Women's Meru Jacket
http://uk.thenorthface.com/tnf-uk-en/women-s/shop-by-category/jackets/summi...
Jacket that are also good but designed more as a mid layer.
These sometimes get used as belay jackets for people who don't need as much warmth or because the warmer jackets out there are all aimed at men.
The North Face Women's RP Optimus Jacket
Montane Women's Flux Jacket
Marmot Women's Dena Jacket
Rab Women's Photon Hoody
Haglofs Barrier II Q Hood (Women's)
Berghaus Women's Ignite Insulated Hoody
Above all I would get to as many shops as possible and try lots of jackets on. Hope this helps.