IMO 300g of concentrate per day is not enough for a GG in kid with 5 weeks to go, but you will have to go with what she eats. Try and include a lot more of veg/fruit - also I already have a good selection of weeds (which mine love - docks, dandelion, ivy of course). Mine (due this weekend) was slowing down a bit, but I have given her some provit dressing on her sugarbeet (also very good for energy for both sheep and goats), and her appetite has improved.
She also loves Readigrass, is currently off oats and mix, but will eat diary nuts and shreds (but not mixed together...). Last week she didn't the dairy nuts (and I don't like giving too much of them as they are 18% protein a but too high I think)....
During the last few weeks goats will not manage to get all their energy needs from hay and a little concentrate, she will need supplementing, especially if she is carrying twins.
You will only really have to worry when she stops eating her concentrates all together or just picks at them and looks in general not be well. I have a bottle of Propylene Glycol (from the vets) ready to drench if necessary, and I do that even before I call for a vet if she stops eating - it doesn't do any harm and will help saving the goat. Same for Calciject - signs of hypocalceamia are her looking quite stiff and having trouble getting up. I had both of them last year...
Re udder - my 2nd kidder GG has had a huge, but soft udder since about 5 weeks before, she was milked until beginning of December then dried off.